The joint military exercises are in response to Japan's nervousness about China's interest in disputed islands in the East China Sea.
A series of unprecedented joint drills, code-named Dawn Blitz, began earlier this month between the United States and Japan off the coast of California with a specific aim: a joint amphibious assault on the island after it has been seized by a small, but heavily armed, invading force.
San Clemente Island, located about 75 miles northwest of San Diego, is acting as a surrogate for the disputed island chain known as the Senkaku Islands in Japan and the Diaoyu in China. Japanese officials insist publicly that the drills are not targeting a third country, adding that the island's identity is purely hypothetical.
The exercise has added to tensions thousands of miles away in waters near the Senkaku Islands, a group of islands in the East China Sea that the Japanese government bought from their private owners last year, triggering violent protests in China and sending Sino-Japanese ties to their lowest point in years.
The ongoing dispute over the territory, and the ease with which Chinese surveillance ships regularly patrol nearby waters, have exposed Japan's vulnerability to an attack on the string of islands on its west and southwest coasts, including Okinawa and the Senkaku Islands. The prospect of armed conflict over the Senkaku Islands has Japan understandably nervous. As Dawn Blitz indicates, developing the ability to defend and retake them has become a priority.
"The defense of remote islands is a pressing issue, but the SDF [Japan's self-defense forces] has just begun training to develop such capabilities, which are required of US Marines," Japan's vice chief of staff, Lt. Gen. Koichi Isobe, told reporters. "Japan needs to determine its defense strategy and procure necessary equipment and train SDF members for this purpose."
The drills, which end later this week, began with an initial assault led by about 80 US Marines and three MV-22 Osprey aircraft, followed by a Japanese amphibious force. In all, Japan has committed about 1,000 troops to the Dawn Blitz operation, along with two warships. Troops from New Zealand and Canada are also taking part.
"I will tell you that I was very impressed with not just the cooperation, but really the operational capabilities that [Japan's self-defense forces or SDF] are starting to bring together," says Brig. Gen. John Broadmeadow, commanding general of the US Marine Corps 1st Marine Expeditionary Brigade.
China had reportedly called on the US and Japan to cancel the operation, which began just two days after Chinese leader Xi Jinping and US President Obama held a summit in California. Tokyo and Washington ignored the request.
An official source familiar with Dawn Blitz conceded that the drills were designed to demonstrate to Beijing that Japan is bolstering its deterrence capability with the help of its US ally.
"We're aware of China's objections, but from a Japanese and US perspective, the object of the exercise is to build a powerful deterrent and demonstrate that the two forces are seamlessly connected – to show the Chinese that they are battle-ready," the source told the Monitor on condition of anonymity because they were not allowed to speak to the media. "There is nothing unusual in that."
China has lodged a protest against the drills.
The country's Foreign Ministry spokesman, Hong Lei, said only that Beijing hoped "the relevant sides can focus on peace and stability in this region, and do more to contribute to mutual trust and regional peace and stability."
Faced with Defense Department budget cuts and a new military focus on the Asia-Pacific, US officials are keen for Japan to play a more active role in the security alliance.
The joint drills are a key part of that strategy, given that Japan does not have its own amphibious assault vehicles.
But the exercises put Washington in a potentially tricky position, say some analysts. Under the US-Japan security treaty it is obliged to help Japan deter an attack on its territory, but it has publicly refused to take sides on the Senkaku island issue. Instead, it has called for calm and encouraged the two sides to hold negotiations.
"I don't think Dawn Blitz puts the US in a tricky position," the official says. "They started the drill just after the Obama-Xi summit to avoid any diplomatic repercussions. But the fact that Japan and the US went ahead with the exercise also sends a message – that they are on the same page when it comes to deterring possible Chinese aggression."
The need to bolster the defense of Japan's outlying islands was first recognized by its last prime minister, the left-of-center Yoshihiko Noda, whose administration effectively nationalized the Senkaku Islands last year.
Under the current prime minister, Shinzo Abe, the need to create a special force, modeled on the US Marines, capable of repelling a Chinese assault on the Senkaku Islands has taken on greater urgency.
Japan raised its defense budget this year for the first time in 11 years, and is expected to devote much of the new funding to expanding the size and scope of the Western Army Infantry Regiment, the name given to a small unit of troops that has been practicing island warfare under the guidance of US Marines at Sasebo naval base in southwestern Japan.
The perceived threat from China to Japan's most vulnerable islands could give Mr. Abe the momentum he needs to dramatically alter Japan's defense posture if, as most observers believe, his Liberal Democratic Party seizes control of both houses of parliament in upper house elections next month.
Later this year, Japanese lawmakers are expected to debate the creation of a White House-style National Security Council and granting Japanese troops the right to engage in collective self-defense, or coming to the aid of the US or other ally under attack.
"I expect Abe to start spending his political capital on his 'values' agenda," says Jun Okumura, a Japan expert at the Eurasia Group. "He won't be able to take his eye off the economy, because the ultimate success of his values agenda will depend on how his economic program is taking effect. But after the upper elections he won't have to go to the polls for three years – that's quite a big window."
In a recent paper for Chatham House, John Swenson-Wright, senior lecturer in modern Japanese politics and international relations at Cambridge University, said Abe's popularity, on the back of his economic program's early success, had enabled him to pursue new security and foreign-policy initiatives.
"In the context of the cold war, successive prime ministers adopted an intentionally restricted role for the security forces," Mr. Swenson-Wright said. "Now, confronted by arguably more immediate and serious security challenges, both in East Asia and farther afield, Abe appears to be promoting a more ambitious and assertive defense posture."