Japan and the United States plan to draw up an operations plan for a combined response by their armed forces to Chinese threats to the Senkaku Islands, government sources said Saturday.

Tokyo and Washington are already discussing how to respond in the event of an emergency on or around the uninhabited islands in the East China Sea, the sources said, and aim to finish crafting the plan by next March.

The administration of U.S. President Donald Trump has said America’s commitment to defend Japan under Article 5 of the two countries’ security treaty extends to the Senkaku Islands. The article obligates the United States to help protect territory under Japanese administration in the case of an armed attack.

But the U.S. government has repeatedly said it will take no position on the issue of sovereignty over the Japan-administrated islands, which China claims and calls the Diaoyu.

By working out a plan to deal with a potential military conflict with China, Japan is hoping the United States will take a more active role regarding the sovereignty issue.

The plan being drawn up assumes such emergencies as armed Chinese fishermen landing on the islands, and Japan’s Self-Defense Forces needing to be mobilized after the situation exceeds the capacity of the police to respond, according to the sources.

The Self-Defense Forces on their own have studied how to respond to such threats. The focus of these intergovernment talks is how to incorporate the U.S. military’s strike capabilities, the sources said.

“Given that military organizations always need to assume the worst possible situation, it is natural for the two countries to work on this kind of plan against China,” said Bonji Ohara, a former naval attache at the Japanese Embassy in Beijing who is now a senior fellow at Sasakawa Peace Foundation, a Japanese think tank.

The negotiations between Japan and the United States have been taking place mainly within the framework newly created by the 2015 defense guidelines, called the Bilateral Planning Mechanism, or BPM.

The guidelines stipulate that the SDF and the U.S. military will “conduct bilateral operations to counter ground attacks against Japan by ground, air, maritime, or amphibious forces.”

The two countries already have combined operations plans in the event of an emergency on the Korean Peninsula and other situations.

Meanwhile, the two countries staged their biggest combat-readiness war game ever in and around Japan, with U.S. fighter jets darting over the Western Pacific on Saturday as the nuclear powered USS Ronald Reagan aircraft carrier joined Japanese destroyers and a Canadian warship.

Japan and the United States have mobilized 57,000 sailors, marines and airmen for the biennial Keen Sword exercise — 11,000 more than in 2016 — with simulated air combat, amphibious landings and ballistic missile defense drills. Japan’s contingent of 47,000 personnel represents a fifth of the nation’s armed forces.

“We are here to stabilize, and preserve our capability should it be needed. Exercises like Keen Sword are exactly the kind of thing we need to do,” Rear Adm. Karl Thomas, the commander of the carrier strike group, said during a news briefing in the Reagan’s forecastle as F-18 fighter jets catapulted off the flight deck above him.

Eight other ships joined the carrier for anti-submarine warfare drills in a show of force in waters that Washington and Tokyo fear will increasingly come under Beijing’s influence.

“The U.S.-Japan alliance is essential for stability in this region and the wider Indo Pacific,” Rear Adm. Hiroshi Egawa, the commander of the Japanese contingent, said aboard the Reagan

Based in Yokosuka, the Reagan is the biggest U.S. warship in Asia, with a crew of 5,000 sailors and around 90 F-18 Super Hornet fighters.

A Canadian naval supply ship is also taking part in Keen Sword, along with the frigate that sailed with the Reagan on Saturday.

Canadian participation is taking a bilateral drill that began in 1986 “into the realm of multilateral exercises,” Canada’s defense attache in Japan, Capt. Hugues Canuel said in Tokyo. Participation in Keen Sword, he added, reflects Canada’s desire to have a military presence in Asia.

Canada isn’t the only Western nation looking to take a bigger security role in the region. Britain and France are also sending more ships as China’s military presence in the South China Sea grows and its influence over the Indo Pacific and its key trade routes expands.

British, French, Australian and South Korean observers will also monitor Keen Sword, which began Monday and ends on Thursday.

Growing foreign interest in Asian security, including North Korea’s development of nuclear weapons and ballistic missiles, coincides with greater Japanese willingness to back up its regional diplomacy with a show of military muscle.

Tokyo this year sent its biggest warship, the Kaga helicopter carrier, on a two-month tour of the Indo-Pacific region, including flag-waving stops in the Philippines, Indonesia, Sri Lanka, India and Singapore.

The 248-meter-long (813.65-foot) Maritime Self Defense Force ship and its two destroyer escorts also conducted drills with a Japanese submarine in the contested South China Sea.

At the same time, Prime Minister Shinzo Abe has engaged China in dialogue to reduce tension between their militaries in the East China Sea and to increase economic cooperation between Asia’s two leading economies.

Amid a background of trade friction with Washington, Abe last month traveled to Beijing, the first such trip by a Japanese leader in seven years, for talks with President Xi Jinping and Premier Li Keqiang. Abe told them that China and Japan shared responsibility for regional security, including tackling the North Korean issue.

Japan, however, still views China as a potentially much larger and more challenging foe than Pyongyang as its expanding navy consolidates control of the South China Sea and ventures deeper into the Western Pacific and Indian Ocean.

Beijing this year plans to spend 1.11 trillion yuan ($160 billion) on its armed forces, more than three times as much as Japan and about a third of what the U.S. pays for a military that helps defend the Japanese islands.

Keen Sword “remains an expression of the commitment of like-minded allies and partners. To really see what we can do in terms of demonstrating advanced capabilities together to ensure peace and stability in the Indo-Pacific,” the chief of U.S. naval operations, Adm. John Richardson, said Thursday from Australia during a telephone news briefing.