By David Scott

Operation Highmast, running from April to November 2025, took a UK Carrier Strike Group (CSG), led by HMS Prince of Wales, over 40,000 nautical miles to the Sea of Japan and back. The CSG consisted of five UK vessels, with eight others joining the CSG at various stages from other navies. Three strategic considerations underpinned this deployment as per Prime Minister Keir Starmer: successfully operating a two-carrier navy (HMS Queen Elizabeth and HMS Prince of Wales), sending a “clear message of strength to our adversaries,” and “a message of unity and purpose to…allies.”

Operating a Two-Carrier Navy

Operation Highmast was announced in May 2023 by Conservative Party Prime Minister Rishi Sunak at the signing of the Hiroshima Accord, which was a landmark agreement focusing on “an enhanced UK-Japan global strategic partnership” and included “the future deployment of the UK Carrier Strike Group to the Indo-Pacific.” The deployment was carried out by the Labour Party administration after it came to power in July 2024, and it proceeded despite some calls to “mothball” of one of the carriers after the exchange of power between parties.

Another strategic decision illuminated by Operation Highmast was that despite growing concerns over Russian aggression in Europe, the Royal Navy maintained an Indo-Pacific commitment, albeit modified. The March 2021 Integrated Review of Security, Defence, Development and Foreign Policy announcement of an “Indo-Pacific tilt” underpinned the Queen Elizabeth CSG deployment in that year’s Operation Fortis. Four years later, the June 2025 Strategic Defence Review mantra of “NATO first does not mean NATO only” guided the Prince of Wales CSG deployment in Operation Highmast.

Strategically, the UK’s punch increased as both its Elizabeth-class aircraft carriers, the HMS Queen Elizabeth and HMS Prince of Wales, are the largest vessels ever constructed for the Royal Navy (80,000 ton displacement). This is almost four times the displacement of the three Invincible-class aircraft carriers (22,000 ton displacement) they replaced. Additionally, the Initial Operating Capacity (IOC) for the Wildcat helicopter Sea Venom anti-ship missile, carried on the Prince of Wales, was announced at the start of October. The Royal Navy considered this “a step-change in [its] combat power.”

After deciding to build the aircraft carriers, the UK government chose to embark F-35B fighters, considerably more advanced than the retired Harriers used on the previous Invincible-class. Strategically, the F-35B decision would enhance interoperability with the US, Italian, and Japanese navies. Eighteen UK F-35Bs embarked at the start of the Prince of Wales deployment and were joined by six more in October for a total of 24. Unfortunately, these jets had embarrassing engine malfunctions including one that was temporarily grounded in India as well as another in Japan. Nevertheless, Full Operational Capacity (FOC) was declared in November, signifying that the two carriers, the Queen Elizabeth and the Prince of Wales, could operate with purely UK F-35B complements.

Working with Allies and Partners

The Royal Navy’s ability to work with others was illustrated in cooperation with various European navies as well as in operations with India, Australia, Japan, and the United States—denoting a tacit balancing against China.

Operation Highmast represented a European rotation of CSGs, under the European Carrier Group Interoperability Initiative (ECGII), which has been guiding defense movements since 2008. The 2023 UK-France Summit had agreed on “the sequencing of more persistent European carrier strike group presence in the Indo-Pacific.” In this vein, the Italian CSG deployment in the second half of 2024, led by ITS Cavour, was followed by the French CSG deployment in the first third of 2025, led by FNS Charles de Gaulle, and then by the UK CSG deployment, led by HMS Prince of Wales, in the following months of 2025.

Operation Highmast had other European nations embedding their ships within the UK CSG. The Norwegian frigate HNoMS Roald Amundsen was in support throughout the CSG deployment. This reflects the Joint Statement on Enhanced Defence Cooperation between Norway and the United Kingdom signed in February 2025. Portugal’s frigate NRP Bartolomeu Dias joined the CSG from the Atlantic to the Mediterranean. Spain’s frigate ESPS Mendez Nunez joined from the Atlantic to the Philippines, and Italy’s ITS Luigi Rizzo joined the CSG in the Mediterranean.

Close UK-Italy ties were on show as Foreign Secretary Yvette Cooper and Defense Secretary John Healey hosted their Italian counterparts on board the Prince of Wales in November at the conclusion of the Falcon Strike exercise, which was the NATO exercise at the end of Operation Highmast of the coast of Naples, Italy. Their Joint Statement noted:

The presence of the F-35-equipped UK Carrier Strike Group in Naples underlines deep British-Italian defense ties. Complex joint exercises during the deployment have further enhanced the interoperability of our Armed Forces.

The dual carrier exercises with Italy’s ITS Cavour in the Med Strike exercise in May as well as the Neptune Strike exercise in November represented a European willingness to carry the burden in the Mediterranean, enabling US carrier strength to be deployed elsewhere.

The UK CSG interaction with India reflected the February 2025 Defense Partnership-India (DP-1) as well as the UK decision in 2022 to co-lead India’s Indo-Pacific Ocean Initiative (IPOI). The CSG exercised in the Arabian Sea with India twice on its way to and from Japan. In June 2025, the CSG exercised with INS Tabar, a P-8I Neptune plane, and an Indian submarine. The October Konkan exercise was particularly powerful. It involved dual carrier operations with the INS Vikrant CSG for the first time, which included seven ships in the Indian CSG and six ships in the UK CSG. Port calls to Mumbai and Goa coincided with Keir Starmer’s visit to Mumbai. Not surprisingly, the India-UK Joint Statement on October 9 declared: “Prime Minister Modi welcomed the port call of UK’s Carrier Strike Group and the Royal Navy’s exercise Konkan with the Indian Navy.” An implementing agreement on electric-powered engines, currently in development by Rolls Royce for India’s next generation navy, was on show with the Prince of Wales’s and HMS Richmond’s Full Electric Propulsion System.

Australian involvement with the CSG was noticeable. Having just carried out freedom of navigation activity around the Spratley Islands with HMS Spey in June, Australia’s HMAS Sydney joined the UK CSG in July on their way to Australia for Exercise Talisman Sabre. The Sydney participated in the CSG exercises in the Timor Sea with the USS George Washington CSG, representing a trilateral Australia-UK-US (AUKUS) format. On July 27, the third day of the Australia-UK Ministerial (AUKMIN) talks were held in Darwin, Australia on the Prince of Wales under Reciprocal Access Agreement (RAA). These talks involved Foreign Secretary David Lammy, Defense Secretary John Healey, and their Australian counterparts. The AUKMIN Joint Statement welcomed that “the [CSG] deployment demonstrates the UK’s ongoing commitment to increase interoperability with Australia in the Indo-Pacific.” HMAS Brisbane joined the CSG in August in the Philippine Sea as part of the trilateral Japan-UK-US CSG and again in the bilateral UK-Japan carrier drills southwest of Japan in September.

UK convening power was on display as—for the first time—the Prince of Wales led the Bersama Lima exercise in September, off the Malaysian coast, under the Five Power Defense Arrangements (FPDA). This involved other naval units from Malaysia, Singapore, Australia (HMAS Ballarat) and New Zealand (HMNZS Aotearoa). New Zealand’s HMNZS Te Kaha had earlier joined the CSG from April to July across the Indian Ocean from the Arabian Sea to the Timor Sea, while Canada’s HMCS Ville de Québec joined the CSG from April (Devonport) to August (North Philippine Sea).

UK cooperation with Japan was further strengthened by Operation Highmast. When the Prince of Wales moored in Tokyo Bay on August 28, UK Defense Secretary John Healey, First Sea Lord General Sir Gwyn Jenkins, and Japan Minister of Defense Gen Nakatani were present to welcome the carrier and participate in the Pacific Future Forum onboard. At the Forum, Healey stressed UK-Japan defense cooperation: “[T]his carrier strike route deployment is the operational demonstration of this truth,” and “that is why the presence of the Prince of Wales here in Tokyo is not just symbolic — it’s strategic.”

Naval cooperation with Japan was on show with the trilateral carrier exercises involving JS Kaga in the North Philippine Sea in August, the F-35B bilateral exercises in the Sea of Japan on September 6, and the bilateral carrier exercise off south-west Japan, which again involved JS Kaga as well as JS Akebono, on September 9. It was particularly helpful to provide proof of concept when UK jets landed on JS Kaga as it was converted from a helicopter carrier to a fixed-wing F-35B-capable aircraft carrier. It was also noticeable that JS Akebono stayed with the UK CSG on its way back across the Indian Ocean.

The trilateral carrier exercise in the North Philippine Sea was a particularly striking visual moment, involving as it did four flat-top F-35B carrying battle groups, involving the USS George Washington, the USS America, Japan’s JS Kaga, and the UK’s Prince of Wales. This trilateral naval format reflects the Japan-UK-US agreement signed by naval chiefs in October 2016, that “as Chiefs of three highly capable and like-minded Services, [the nations] share a common vision of enhancing the operational effectiveness of… maritime forces through increased cooperation.” This was furthered in their Joint Statement in November 2019 about maintaining a “routine forward presence“ for cooperating over “the security of the Indo-Pacific region.” In the case of operational effectiveness, the common F-35B choices made by all three navies aids inter-operability, which was very much on show with the crossdeck activities carried out in Operation Highmast between these various carriers.

Last but not least, cooperation with the US was present throughout. The UK CSG was led through the Bab-el-Mandeb by USS Truxtun. Twice the USS George Washington CSG exercised with the UK CSG: once bilaterally in the East Timor Sea and another time trilaterally with Japan in the Philippine Sea. In another first, the USNS Wally Schirra, alongside RFA Tidespring, carried out a simultaneous Replenishment at Sea (RAS) with the Prince of Wales. The USS Higgins accompanied HMS Richmond on its transit of the Taiwan Strait in September before briefly joining the main UK CSG group as it sailed across the South China Sea. When the CSG transited into Red Sea in October, anti-drone and missile cover was provided by USS Forrest Sherman.

Deterring Adversaries?

On the eve of departure, the UK Defense Secretary John Healey had been upbeat in April, commenting, “[The] Royal Navy is once again demonstrating its formidable capability while protecting British values and sending a powerful message of deterrence to any adversary.”

In terms of operations, the CSG was able to twice deploy through the troubled Red Sea. When transiting in late May/early June, the CSG had been put on “defense station” in the light of continuing Houthi activities in the Red Sea. The context was that the UK had carried out strikes on Houthi drone facilities on April 29, joining the US in Operation Rough Rider. However, despite Houthi outrage, all was calm a month later for the CSG. Upon the CSG’s return in September, a diversionary tactic was employed. A fake Bahr Guardian sea exercise was announced for the Arabian Sea, with an accompanying press blackout, leaving the CSG free to instead slip though the Bab-el-Mandeb and up the Red Sea. It is unclear as to whether this move was an indication of the UK’s cunning  or a fear that a publicly announced transit was still too dangerous.

China remained the elephant in the room as the UK refused to acknowledge the deployment was China-motivated. Though China did not use official public channels to announce its displeasure, its state media, namely the Global Times, was ready to express China’s negative opinions. Back in 2023, when the deployment was first announced, a Global Times editorial on December 17, titled “The UK’s sunset fleet should just stay surfacing the internet,” warned that the UK was “closer to becoming a laughing stock.” The article derided UK collaboration with Japan as a vain attempt to restrain China. These protestations more likely revealed a sensitive subject for Beijing over UK-Japan security collaboration.

During the 2025 CSG deployment, the Chinese state media was ready to comment again. Starmer’s announcement about meeting threats was immediately denounced in the Global Times on April 24 with a piece titled “Can the UK aircraft carrier’s ‘return to the Indo-Pacific’ deter anyone?” Global Times journalists, Liu Xuanzun and Liang Rui, scoffed over UK problems with the F-35B jets in their August 10 article titled: “UK carrier-based F-35B reportedly makes emergency landing in Japan; Chinese expert says incidents highlight Britain’s struggling with aircraft complexity.”

There had been advance speculation whether the UK would be deterred from freedom of navigation activities in the Taiwan Strait and the South China Sea. It was significant that both were carried out. The CSG detached HMS Richmond for a transit of the Taiwan Strait alongside USS Higgins on September 12, which was immediately denounced as “provocative” by the PLA Eastern Theater Command. Some Chinese harassment had taken place. “Constructive kills,” or in layman’s terms tactical drills run with no missiles fired, were carried out around HMS Richmond with Chinese jets following the path they would take if they were launching an attack. Immediately after, the CSG transited the South China Sea, during which RFA Tidespring and HNoMS Roald Amundsen carried out specific freedom of navigation activities around the Spratleys in mid-September. The CSG was followed by several Chinese ships broadcasting messages for the CSG to stay away. However, the details on this only came to light in a Times report on September 29 followed by the Royal Navy briefing on 30 September, by which time the UK ships had long left these waters.

Unsurprisingly, the UK exercising with other China-concerned actors attracted further criticisms from China. On July 14, Zhang Changyue and Guo Yuandan denounced the Talisman Sabre exercise in their piece titled: “US-Australia largest ever war drill underway, hyping it may draw ‘Chinese observation’ to boost attention.” The subsequent trilateral exercising drew more Chinese fire with Liu Xuanzun and Liang Rui’s piece on August 6 titled: “US, UK, Japan, others hold drill in Pacific; move undermining regional peace.” One can surmise that such Chinese criticisms would not appear unless the UK deployment was having an impact regarding freedom of navigation issues and a tacit balancing of China.

Looking forward

Five strategic questions remain to be answered for the future concerning the operation of a two-carrier Navy:

1. With two carriers scheduled for active service until 2029, should the UK maintain a two-carrier navy and resist any further calls for ”mothballing?”
2. What is the right balance between Euro-Atlantic and Indo-Pacific CSG deployments? If Indo-Pacific deployments continue regularly should the four-year gap between Queen Elizabeth and Prince of Wales missions become the norm, or should it be shortened or lengthened?
3. How far should carriers operate as “crewed aircraft” carriers. The Strategic Defence Review recommends that:

Much more rapid progress is needed in its evolution into ‘hybrid’ carrier airwings, whereby crewed combat aircraft (F-35B) are complemented by autonomous collaborative platforms in the air, and expendable, single-use drones. Plans for the hybrid carrier airwings should also include long-range precision missiles capable of being fired from the carrier deck.

It can be noted that in a “historic first,” the Prince of Wales used drones to transfer supplies between ships as opposed to traditional helicopters.

4. How will the Royal Navy manage its fleet’s numbers to support its strategic goals? The structural problems of being hollowed out, in terms of other naval assets, remain acute. The continuing challenge of numbers expected to decline before eventual increase in numbers as eight Type-26 and five Type-31 replacements for the nine current Type-23 frigates are completed.
5. How will the Royal Navy manage its new F-35Bs moving forward? Questions and choices still remain surrounding the numbers and capabilities of the F-35B planes. At present, the UK currently has 34 F-35Bs with initial plans to acquire 48 and potentially 138 in the more distant future. F-35B capabilities await the replacement of their Paveway-series guided bombs by more advanced Spear-3 cruise missiles. These were originally slated for delivery and use on F-35Bs by 2025 but face delays due to software configuration problems at Lockheed Martin and US export control regulations.

“Quo Vadis?” indeed, for a two-carrier UK navy.

Dr. David Scott is an associate member of the Corbett Centre for Maritime Policy Studies. A prolific writer on Indo-Pacific maritime geopolitics, he can be contacted at davidscott366@outlook.com.

Featured Image The U.K. Queen Elizabeth-class (QEC) aircraft carrier HMS Prince of Wales (R09)’s participation in WESTLANT 23. (US Navy photo by Dane Wiedmann)

By Michael Hanson

The world took note of the meteoric growth of China’s People’s Liberation Army (PLA), both in size and capability. Specifically, the PLA and PLAN’s amphibious capabilities development is impressive and alarming. According to many experts, the reason for this rapid development is the forceful reintegration of the island of Taiwan into the People’s Republic of China (PRC).¹ Analysts argue that a PLA cross-strait amphibious invasion of Taiwan would be the largest amphibious assault in history, greater in scale and complexity than invasions of Normandy and Okinawa, the largest amphibious operations in each theater during World War II.²

A cross-strait operation would be a serious challenge for a world-class military. Though the Chinese military is quickly reaching peer status with the United States military in many areas, the PLA is not currently ready for a daunting amphibious invasion of Taiwan. The PLA remains untested. Chinese leaders will likely subject their prototype to a series of test runs before committing to such a fateful mission. History and current events show small wars and limited interventions serve as useful training grounds to develop the leadership, processes, and capabilities of military forces for larger designs. At present, North Korean troops are active participants in the war in Ukraine to presumably gain combat experience of their own.³ Likewise, before China embarks on a major war, it will likely hone its edge in small ones.

According to the renowned military historian Basil H. Liddell Hart, “A landing on a foreign coast in the face of hostile troops has always been one of the most difficult operations of war.”⁴ To establish a lodgment, not only does the offensive force have to overcome a defending force, but significant geographic and climatic factors. Once successfully seizing a beachhead, the attacker must break out from it and begin a land campaign in which it can still meet defeat if it does not have adequate logistics to sustain its campaign. Even once ashore, the challenges of sustaining a campaign overseas are significantly greater than doing so overland. It is for these reasons that successful amphibious campaigns have been the domain of a relatively few militaries in modern history.

China seeks to join the small pantheon of militaries effective at amphibious operations. However, China’s military last combat experience occurred during the Sino-Vietnamese War of 1979. In that conflict Vietnamese militias stymied Chinese offensive thrusts while the bulk of Vietnam’s People’s Revolutionary Army was simultaneously engaged in Cambodia. Though the Chinese never officially acknowledged their casualty figures, independent estimates contend China suffered up to 25,000 killed in action and 37,000 wounded in the month-long war.⁵

The PLA made enormous strides in the 45 years since its last war. In 1979, China possessed a peasant army organized and equipped for what Mao Zedong called “Peoples’ War,” or guerrilla war.⁶ However, modern conflict changed China’s calculus. Following the American overwhelming triumph in the 1991 Persian Gulf War, China embarked on a massive military modernization.⁷ Chinese President Xi Jinping, recently charged the PLA to prepare for war, even uttering the words “dare to fight” during a visit to the Eastern Theater Command, the military district responsible for Taiwan.^8,9 Experts assert President Xi is referring to forceful reunification of Taiwan.¹⁰

Before undertaking such an enormous and consequential operation the PLA must demonstrate its proficiency. China has conducted numerous exercises and drills, but these displays of military might will not prove sufficient. ¹¹ The crucible of real combat must test PLA leadership, units, and operational methods before attempting an invasion of Taiwan. China’s adversaries should remain attuned to China’s engagement in small wars as means to advance political objectives and test its forces in preparation for a Taiwan invasion.

Contingency operations provide a wealth of knowledge and experience. For these reasons, these limited engagements serve as the most effective training operations. Indeed, throughout history countries have used active battlefields as schoolhouses for improving their combat capabilities, especially engaging in small wars to prepare for a larger one.

From 1937 to 1939, civil war raged in Spain and outside powers supplied troops and equipment to both sides. Though volunteers came to Spain from around the world, Germany, Italy, and the Soviet Union provided support with the express purpose of gaining knowledge and experience, and testing equipment and doctrinal methods with an eye on the future. Germany, rearming from the severe restrictions of the Treaty of Versailles, exploited this opportunity to test its new tanks and airplanes, while employing new concepts.¹² Germany’s famed Condor Legion, a unit consisting of both air and ground elements, was the vessel that gave some 19,000 German soldiers and airmen experience in a warzone.¹³ This was to be an investment that would pay off handsomely in a few short years.

As German arms and ideas were subjected to experimentation in Spain, the Wehrmacht learned other valuable lessons during Adolf Hitler’s bloodless conquests. In Germany’s remilitarization of the Rhineland, as well as its annexations of Austria, the Sudetenland, the rest of Czechoslovakia, and finally Klaipeda, the Wehrmacht gained valuable experience in these unopposed invasions. These campaigns without battles allowed the German military to execute planned movements to seize objectives and secure key terrain and critical infrastructure. The Germans employed tactical and operational methods to set conditions for mutual support when contested. Though the Germans faced little opposition, they experienced other friction and fog inherent in war. In the process of working through these challenges, the Germans profited enormously, specifically in the areas of mobilization, deployment, logistics, and command and control.¹⁴

The United States, in fact, has a long history of developing its military in small wars close to home, but perhaps the most notable are in the period between the world wars known as the Banana Wars. Many American senior commanders in World War II cut their teeth as junior officers in these Latin American interventions, from the soldiers who chased Pancho Villa on the Mexican Border just before World War I, to the Marines who fought bandits in Haiti, Santo Domingo, and Nicaragua during the interwar period. More notable than the personalities who served in these small wars are the lessons in warfighting they brought back with them, such as the Marine development of close air support to tactics in jungle fighting that the “Old Breed” passed to their new recruits in preparation for Guadalcanal.¹⁵

More recent small-scale interventions in America’s near abroad have had notable impacts on the American military as well. Early confusion in Operation Urgent Fury in Grenada exposed gaps in intelligence, planning, and joint interoperability in execution that helped instigate the reforms of the Goldwater-Nichols Department of Defense Act which dictate high level organizations and processes to this day.¹⁶ On the other hand, the rapid success of Operation Just Cause in Panama seemed to validate doctrinal planning and training methods.¹⁷ Both short and decisive operations did much to improve America’s military stature in the rough wake of the Vietnam War.

Other countries have learned from limited adventures abroad as well. The severe shortcomings of Russia’s 2008 invasion of Georgia with its rusty leftover Soviet military served as a wake-up call to President Vladimir Putin. The poor performance of Russian leaders, personnel, units, equipment, and procedures led to massive overhaul of the Russian Army, with a modernization program to upgrade all of these areas of disappointment.¹⁸ After several years of development, President Putin utilized Syria as a testing ground for new Russian weapons as well as a stage to advertise their capabilities to the world.¹⁹ The results of this build-up, combined with Russia’s initial proxy war in Ukraine, served to convince the world of a daunting Russian military machine, an image that was only dashed when Putin squandered these reforms with his ill-advised and poorly planned conventional invasion of Ukraine in 2022.

Yet while the Russian war machine is bogged down in cratered and shell-blasted Ukrainian landscapes reminiscent of the battlefields of World War I, China continues developing its own capabilities. Chinese military spending rose significantly in 2024 to $236 billion.²⁰ Recent Chinese developments include the 2022 launch of a Type-003 Fujian aircraft carrier, comparable to an American Nimitz class super carrier.²¹ In addition to this crown jewel of power projection, the PRC launched their fourth Type 075 Helicopter Landing Dock (LHD) ship, comparable to the American Tarawa and Wasp class amphibious ships, and other amphibious dock landing ships that complement this platform to round out the Amphibious Ready Group construct.²² Like the American Marine Expeditionary Units (MEUs), these acquisitions give China a suite of crisis response and power projection capabilities. They have even built several classes of at-sea replenishment ships to support their fleet far from home waters.²³

The question remains whether platforms similar to Nimitz class aircraft carriers, Tarawa/Wasp Class helicopter ships, and underway replenishment ships are necessary for a cross-strait invasion of Taiwan when the island is already within range of airfields on the Chinese mainland. More likely these are intended for power projection in their near abroad. In other words, the world may witness a coming era of Chinese gunboat diplomacy and small war interventions similar to the Banana Wars during the period of rising American hegemony. With over $1 trillion invested since 2013 and as of 2023, 147 countries signing on to the Belt and Road Initiative, China has lots of opportunities to intervene in overseas contingencies to defend its national interests.²⁴ In line with former Chinese President Hu Jintao’s call for the People’s Liberation Army Navy (PLAN) to conduct “new historic missions,” the PLAN is already at work flexing its muscles abroad.²⁵

Since 2009 the PLAN has participated in international counter-piracy operations in areas such as the Gulf of Aden, Bab-el-Mandeb, and Arabian Sea.²⁶ Since the start of the Israel-Gaza War, the PLAN dispatched naval forces to the region following Houthi attacks on merchant ships in the waters off of Yemen.²⁷ While the PLAN routinely operates from a military base in Djibouti, one expert warns this outpost will only be the first of many Chinese overseas military bases.^{28, 29} Yet Chinese involvement in multilateral military missions extend to the land as well.

In recent years, over 2,000 Chinese troops deployed to conflict zones in Mali, Darfur, South Sudan, and the Democratic Republic of the Congo.³⁰ These deployments are not a recent developments. Since 1992, China has deployed over 50,000 troops to no less than 29 United Nations peacekeeping missions, losing 24 killed in these operations.³¹ Of the permanent members of the UN Security Council, China contributes the most personnel to UN missions. President Xi Jinping offered to provide 8,000 troops to a United Nations standby force in 2015.³² As Chinese sailors, soldiers, and airmen gain experience in overseas contingencies, the Chinese military builds its capability to pursue larger missions, like an invasion of Taiwan.

Conclusion

The world has time before China could attempt to use force to bring Taiwan under its heel. However, every year that passes, they increase their readiness. Drills and training exercises certainly increase a military’s abilities. However, only so much can be learned in sterile, controlled training environments. China will likely test its military might in small wars before embarking on a larger one. The world should take note of China’s entry and actions during a small war. When the People’s Republic of China does engage in a small war, the world will know China is preparing for the forceful reunification of Taiwan.

Major Michael A. Hanson, USMC, is an Infantry Officer serving at The Basic School, where the Marine Corps trains its lieutenants and warrant officers in character, officership, and the skills required of a provisional rifle platoon commander. He is also a member of the Connecting File, a Substack newsletter that shares material on tactics, techniques, procedures, and leadership for Marines at the infantry battalion level and below.

References

[1] Ian Easton, The Chinese Invasion Threat, (Manchester, UK: Eastbridge Books, 2017) Foreward.

[2] Council on Foreign Relations. “Why China Would Struggle To Invade Taiwan.” https://www.cfr.org/article/why-china-would-struggle-invade-taiwan. Accessed March 26, 2024.

[3] Karolina Hird, Daniel Shats, and Alison O’Neil, “North Korea Joins Russia’s War Against Ukraine: Operational and Strategic Implications in Ukraine and Northeast Asia,” Institute for the Study of War, last updated October 25, 2024. https://www.understandingwar.org/backgrounder/north-korea-joins-russias-war-against-ukraine-operational-and-strategic-implications. Accessed July 31, 2025.

[4] Joint Chiefs of Staff, Amphibious Operations, JP 3-02 (Washington, DC: Joint Staff, 21 January 2021). I-1.

https://www.jcs.mil/Portals/36/Documents/Doctrine/pubs/jp3_02.pdf. Accessed March 26, 2024.

[5] Zhang Xiaoming, “China’s 1979 War with Vietnam: A Reassessment,” The China Quarterly 184 (Dec 2005)

[6] Edmund J. Burke, Kristen Gunness, Cortez A. Cooper III, Mark Cozad, People’s Liberation Army Operational Concepts, (RAND Corporation, 2020). 4.

[7] Edmund J. Burke, Kristen Gunness, Cortez A. Cooper III, Mark Cozad, People’s Liberation Army Operational Concepts. 4.

[8] Miriah Davis, “President Xi Jinping orders Chinese military to prepare for war over concerns national security is ‘increasingly unstable, uncertain’”, Sky News Australia, November 9, 2022. https://www.skynews.com.au/world-news/president-xi-jinping-orders-chinese-military-to-prepare-for-war-over-concerns-national-security-is-increasingly-unstable-uncertain/news-story/db8ca191e86fd81a23b3b794ff4f2a0e. Accessed March 26, 2024.

[9] “China’s Xi Jinping says army must ‘dare to fight’ during military inspection,” The Straits Times, last updated July 6, 2023. https://www.straitstimes.com/asia/east-asia/chinas-xi-jinping-says-army-must-dare-to-fight-during-military-inspection. Accessed March 26, 2024.

[10] Brad Dress, “China will be ready for potential Taiwan invasion by 2027, US admiral warns,” The Hill, March 21, 2024. https://www.msn.com/en-us/news/other/china-will-be-ready-for-potential-taiwan-invasion-by-2027-us-admiral-warns/ar-BB1kjib7. Accessed March 26, 2024.

[11] Kristin Huang, “Chinese military drills simulate amphibious landing and island seizure in battle conditions,” South China Morning Post, July 28, 2021. https://www.scmp.com/news/china/military/article/3142851/chinese-military-drills-simulate-amphibious-landing-and-island. Accessed March 26, 2024;

[12] John T. Hendriz, “The Interwar Army and Mechanization: The American Approach,” Journal of Strategic Studies 16:1 (1993). 87-88.

[13] John T. Correll, “The Condor Legion,” Air & Space Forces Magazine, February 1, 2013. https://www.airandspaceforces.com/article/0213condor/. Accessed March 26, 2024.

[14] Williamson Murray, The Change in the European Balance of Power, 1938-1939: The Path to Ruin, (Princeton, NJ: Princeton University Press, 1984) 152-153.

[15] Mark R. Folse, “Never Known a Day of Peace,” Naval History 35:4, August 2021. https://www.usni.org/magazines/naval-history-magazine/2021/august/never-known-day-peace. Accessed March 26, 2024; Joseph H. Alexander, “Close Air Support: The Pioneering Years,” Naval History 26:6, November 2012. https://www.usni.org/magazines/naval-history-magazine/2012/november/close-air-support-pioneering-years. Accessed March 27, 2024.

[16] Ronald H. Cole, Operation Urgent Fury, (Washington, DC, Office of the Chairman of the Joint Chiefs of Staff, 1997). 6. https://www.jcs.mil/Portals/36/Documents/History/Monographs/Urgent_Fury.pdf. Accessed March 27, 2024;

Daniel Bolger, “Operation Urgent Fury and its Critics,” Military Review LXVI:7, July 1986. https://www.armyupress.army.mil/Journals/Military-Review/Directors-Select-Articles/Operation-Urgent-Fury/. Accessed March 27, 2024;

John J. Hamre, “Reflections: Looking Back at the Need for Goldwater-Nichols,” Center For Strategic & International Studies, January 27, 2016. https://www.csis.org/analysis/reflections-looking-back-need-goldwater-nichols. Accessed March 27, 2024.

[17] R. Cody Phillips, “CMH PUB No. 70-85-1 Operation Just Cause: The Incursion Into Panama,” U.S. Army Center for Military History 2004, 47-48. https://history.army.mil/html/books/070/70-85-1/cmhPub_70-85-1.pdf. Accessed March 27, 2024.

[18] Ariel Cohen Dr. and Robert E. Hamilton Colonel, The Russian Military and the Georgia War: Lessons and Implications (US Army War College Press, 2011), 49-54. https://press.armywarcollege.edu/monographs/576. Accessed March 27, 2024.

[19] Lester Grau and Charles Bartles, “The Russian Ground-Based Contingent in Syria,” Russia’s War in Syria: Assessing Russian Military Capabilities and Lessons Learned (Philadelphia, PA: Foreign Policy Research Institute, 2020) 68. https://www.fpri.org/wp-content/uploads/2020/09/russias-war-in-syria.pdf. Accessed March 26, 2024:

Anton Lavrov, “Russian Aerial Operations in the Syrian War,” Russia’s War in Syria: Assessing Russian Military Capabilities and Lessons Learned (Philadelphia, PA: Foreign Policy Research Institute, 2020) 93. https://www.fpri.org/wp-content/uploads/2020/09/russias-war-in-syria.pdf. Accessed March 27, 2024.

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Featured Image: Rigged with combat loads, paratroopers assigned to a brigade under the Chinese PLA Army file into a Mi-171E transport helicopter during a parachute training exercise in September 2025. (Photo via eng.chinamil.com.cn/by Hu Qiwu)

By Ryan Martinson

Today, Chinese underwater gliders operate throughout the Indo-Pacific, from the Bay of Bengal to the Bering Sea, from high seas to sovereign waters. These winged, torpedo-like submersibles are being deployed in droves to collect information about the marine environment. Traveling underwater in a vertical sawtooth pattern, gliders use onboard sensors to measure characteristics of the ocean such as temperature, salinity, dissolved oxygen, and current speed at different depths to generate water column profiles. This data indirectly bolsters the capabilities of the People’s Liberation Army Navy (PLAN) by expanding its tactical understanding of the ocean environment.

Scientists and engineers based in the People’s Republic of China (PRC) are also developing a new generation of gliders that could play a far more direct role in naval combat by detecting enemy submarines. Since 2014, experts at the PLAN Submarine Academy, working with colleagues at civilian institutions, have been equipping Chinese gliders with passive acoustic sensors. Chinese language records of their activities show a determined effort to adapt this technology for anti-submarine warfare (ASW), an enduring weakness for the PLAN—one that, if remedied, could shake U.S. conventional deterrence in the Western Pacific.

Why Gliders?

The PLAN has a very difficult time detecting advanced foreign submarines within Chinese-claimed maritime space. Modern submarines are stealthy, the ocean is vast and complex, and ASW is inherently difficult—for any navy. But the stakes are especially high for China, given the perceived threat that foreign submarines pose to China’s maritime security. PRC experts often lament that China’s “underwater front door is wide open” (水下国门洞开). China’s 13^th Five Year Plan for Innovation in Marine Science and Technology frankly admitted that China “still lacks the ability to resist hostile threats from the deep sea.” One PLAN analyst declared, “the threats our country faces in the maritime direction mainly come from the undersea [domain], and the main gap with the powerful enemy [the U.S.] is also in the undersea [domain].”

To shrink this capability gap, the PRC has invested heavily in new ASW capabilities for its fleet while looking to the U.S. Navy as a model. The PLAN has built ocean surveillance vessels like the USNS Effective to tow acoustic sensors designed to detect submarines. The PLAN has also procured sub-hunting maritime patrol aircraft, similar to the U.S. Navy’s P-3 “Orion,” and it may soon begin equipping the fleet with an ASW variant of the Z-20 helicopter, often described as a close copy of the MH-60 “Seahawk.”

The PRC is also taking steps to build a network of sensors, some mobile and some fixed, to detect foreign submarines in operationally important areas. Together, these sensors would constitute an “undersea alert system” (水下警戒体系). Some ASW platforms use traditional hydrophones, which only capture information about the frequency (hertz) and intensity (decibels) of sound. However, to localize the source of the sound, multiple hydrophones are often combined into an array, which can be large and unwieldy. A single vector sensor, in contrast, is capable of determining the direction of a sound source. China is very keen on pursuing a new generation of piezoelectric vector sensors, which are far smaller than previous types. Their compact size also allows their installation on much smaller platforms like underwater gliders.

Gliders move up and down in the water column by adjusting their buoyancy while their “wings” enable them to move forward at an angle. As ASW platforms, gliders offer several advantages. Due to their low power requirements, some gliders can operate at sea for months at a time. Because of the simplicity of their design, gliders are also comparatively cheap—an important attribute since they must be deployed in large numbers to be effective. Unlike fixed undersea sensors, gliders can move to where they are needed (albeit very slowly, at just about one knot). Lastly, gliders can maintain regular communications with their operators by transmitting their location (and other information) and receiving new commands when they surface at the end of a dive.

How might the PLAN use acoustic gliders? According to the PLAN researchers working on the project discussed in this article, they would be used to “complete tasks such as autonomous detection, tracking, attribute discrimination, and sending back information on moving targets in sensitive waters or areas of denial (拒止区域).” The program director, Rear Admiral Da Lianglong, likened them to a front-door “security system” (安保系统). One of his briefing slides from a 2019 presentation suggests that the PLAN intends to deploy them in the relatively quiet, deeper waters of the Philippine Sea and northern South China Sea, operationally-important areas where China lacks islands to build fixed undersea arrays.

The Dolphin Project

While the advantages of gliders seem obvious, there are also many technical challenges that must be overcome before they can be used in ASW. Since 2014, the PLAN Submarine Academy, working in conjunction with scientists and engineers from Tianjin University and the Qingdao Pilot National Lab for Marine Science and Technology have methodically surmounted many of these challenges and now possess a capable prototype glider, the “Dolphin,” which has already undergone several rounds of testing in the South China Sea.

The Dolphin is based on the Haiyan glider developed by researchers at Tianjin University. Like most sea gliders, the Haiyan is a tubular robot with wings and a visible antenna. However, it is somewhat unusual in that it is equipped with a small propeller, a useful feature if needed to surface quickly in the event of a potential submarine contact. Chinese oceanographers have already deployed Haiyan gliders within the first island chain and beyond. A specially designed Haiyan variant (Haiyan-X) is capable of diving to tremendous depths, including the bottom of the Mariana Trench. Another variant (Haiyan-L) has been built for greater endurance, purportedly up to five months of continuous operations.

The Dolphin looks like a typical Haiyan glider, except for a vector sensor protruding from its nose. Within the body of the glider, forward of the batteries, is its signal processor. indicating that the platform is designed to autonomously detect, classify, and locate undersea targets, not merely to record and transmit raw data for interpretation elsewhere.

The Dolphin project is led by the Naval Undersea Warfare Environmental Research Institute (海军水下作战环境研究所) at the PLAN Submarine Academy. It is overseen by the Institute’s Director, Rear Admiral Da Lianglong, perhaps the PLAN’s most accomplished expert on undersea science and technology. Rear Admiral Da has won numerous national, provincial, and military awards for his work on how the undersea environment affects sonar performance and submarine tactics.

Under Rear Admiral Da’s leadership, the Environmental Research Institute has shrewdly leveraged civilian organizations to help advance its mission. In 2013, his institute turned its attention to vector sensors. Then, in 2016, it joined with the Qingdao Pilot National Lab for Marine Science and Technology to create the Joint Lab for Civil Military Integration in Qingdao, with Rear Admiral Da as its director. This allows the Submarine Academy to benefit from the expertise, access, and resources available to the civilian marine science community. When Xi Jinping visited the Qingdao Pilot National Lab in June 2018, he spoke about the importance of civil-military integration in marine science. Rear Admiral Da stood beaming in the audience, the embodiment of Xi’s ideal.

Milestones

The team at the Submarine Academy overcame several technical challenges to make the Dolphin a viable ASW platform including self-noise, contact localization fidelity, and overcoming the immense pressure water pressure of deep dives.

The first was self-noise. Researchers originally built the Haiyan glider for oceanographic research, where self-noise is far less of a concern. However, when detecting submarines, it is vital that an ASW platform be as quiet as possible to make it easier to distinguish the relevant signatures from other noises and thereby maximizing the signal to noise ratio. This is especially important when that signature is extremely faint, like those emitted by modern submarines.  

The Haiyan produces noise at the bottom of its dive, when a pump activates to increase buoyancy needed for the ascent. It also produces noise when the propeller engages. These noise problems, however, are simple fixes since the glider can be programmed to turn off its vector sensor during the brief periods when the pump and propeller are on. For the Chinese researchers, the real challenge was reducing the noise generated by the mechanisms used to maintain the glider’s course and attitude. Researched overcame this challenge by changing the position of the glider’s internal battery packs. Through a series of tests conducted at first in specially designed pools followed later by tests in the South China Sea, the researchers were able to optimize attitude and course adjustment mechanisms to reduce this self-noise.

Slight changes to the attitude of the glider presented a second challenge that had to be overcome: errant localization. The vector sensor receives data about the direction of a target in relationship to the attitude of the sensor at the time of detection. For this information to be tactically valuable, the glider required a tiny attitude sensor that would enable an onboard computer to locate the target relative to the surface of the ocean. Scientists at the PLAN Submarine Academy, including Da Lianglong himself, successfully developed a sensor for this purpose and it now equips the Dolphin glider.

Finally, Chinese scientists also had to develop a vector sensor that could reliably operate in the high-pressure environment of the deep ocean. Since many countries prohibit the sale of acoustic sensors to China, researchers could not simply import a foreign product. Since the early 2000s, experts at Harbin Engineering University have conducted pathbreaking research on vector sensors. The team at the Submarine Academy built off their work to develop a deep water vector sensor. In 2019, researchers tested the new sensor in the South China Sea at depths of 800 meters and 1,200 meters with promising results. That same year, Rear Admiral Da and several other colleagues at the Submarine Academy patented a vector sensor that could effectively operate down to 4,000 meters. According to their patent application, the sensor could be particularly suited for unmanned platforms like gliders “for use in submarine detection.”

Since 2018, the Dolphin has undergone multiple tests in the South China Sea, in the deep water northwest of the Paracel Islands. To date, Chinese researchers have only tested the glider’s ability to detect surface ships, which are obviously much louder than submarines. Two series of tests conducted in May and June of 2018 focused on reducing self-noise. Since then, the team has sought to refine the capabilities of the glider’s onboard systems. The most recent known tests conducted in January of 2020 offer a gauge of the Dolphin’s current capabilities. They also show the scale of the PLAN’s commitment to developing these platforms.

During the January 2020 tests, a Dolphin glider successfully tracked the movements of a 50 meter research ship (Haili) traveling at 8 knots at a maximum range of 6.5 km. As part of the same series of tests, a Dolphin glider also tracked a 60-meter merchant ship traveling at 11.7 knots at a maximum range of 11.4 km. The Dolphin also tracked the movements of a 192-meter container ship traveling at 15 knots at a maximum range of 11.2 km. Additionally, in January of 2020, a Dolphin glider tracked a 99-meter rescue and salvage ship, the Nanhaijiu 116, steaming at 14 knots at a maximum detection range of 14.4 km.

Next Steps

To be effective, a glider like the Dolphin would need to work in concert with other such platforms. A single glider would not be enough, since detection ranges will be very short and gliders are not very mobile. The PLAN will likely want to fill an operationally important area of the ocean with dozens of gliders, which will need to be coordinated to ensure efficient coverage. This will be further complicated by the fact that gliders, due to their slow speeds, are vulnerable to undersea and surface currents. Therefore, if one glider drifts out of a given area, another glider will need to move in to fill the gap. Researchers at the Submarine Academy and the Qingdao Pilot National Lab already completed simulations to address the challenge of optimizing the deployment of multiple gliders for target detection. However, these efforts have not yet been tested at sea.

Another challenge is autonomy in signal processing. Gliders will need to analyze the raw acoustic data they receive and determine if what they are “hearing” contains the signature of a target of interest. That task is fairly easy if the target is a 190-meter commercial ship traveling at 12 knots. But it becomes extremely difficult when it is a modern submarine operating at slow speed in the noisy waters of the South China Sea. Detecting and classifying targets has traditionally required humans (i.e., sonar technicians) in the loop. Developing systems that can mimic human intelligence will be vital for any autonomous ASW platform, and Chinese experts have been working on this problem for years, again, most notably at the Harbin University of Engineering. Researchers there claim they have developed unmanned platforms capable of autonomously detecting surface and undersea targets at long range and have tested them in lakes and at sea. In October 2018, the University signed a cooperative agreement with the Submarine Academy, although it remains uncertain if this will include collaboration on underwater gliders. In the meantime, researchers from the PLAN Submarine Academy and the Qingdao Pilot National Lab are proceeding with their own efforts to improve autonomy in target detection.

This relates to another huge challenge of filtering out false detections. Failing to detect an enemy submarine is bad, but declaring the presence of an enemy submarine where none exists could be potentially worse for the PLAN. It might deploy manned ASW assets to the area of false contact, wasting time and resources. Acoustic gliders will likely not be deployed for real-world operations until the PLAN is reasonably certain that onboard systems are sophisticated enough to keep false detections to an absolute minimum. In this situation, redundancy in the undersea alert system (i.e., many sensors in a given area) could help strengthen confidence in a target detection.

Conclusion

Writing in early 2013, before substantive work on acoustic gliders began in China, an expert at the 710 Research Institute boldly predicted—in his words, “without the least bit of exaggeration”—that the future development of underwater gliders would leave submarines with “no place to hide” (无处遁形). Almost ten years later, the PRC is still nowhere close to that. However, the PLAN has come a long way in a short period of time. This achievement has been made possible through a talented, dedicated, and well-funded research team at the PLAN Submarine Academy, a successful approach to civil-military integration, and institutional commitment to redressing China’s weaknesses in ASW. China now possesses a viable prototype acoustic glider that has undergone multiple rounds of testing in the South China Sea. China clearly intends to shut its “underwater front door,” and acoustic gliders will be one tool that helps it do just that.

Ryan D. Martinson is a researcher in the China Maritime Studies Institute at the Naval War College. He holds a master’s degree from the Fletcher School of Law and Diplomacy at Tufts University and a bachelor’s of science from Union College. Martinson has also studied at Fudan University, the Beijing Language and Culture University, and the Hopkins-Nanjing Center.

Featured Image: The guided-missile frigate Zhoushan (Hull 529), together with the guided-missile destroyers Taizhou (Hull 138) and Hangzhou (Hull 136), steam to designated sea area in East China Sea during a maritime training exercise in early January, 2021. (eng.chinamil.com.cn/Photo by Liu Yaxun)