Japan's Maritime Self-Defense Force Submarine Sinks USS Juneau in a New Phase of Japan-U.S. ASW at Valiant Shield 26

On June 27, the retired U.S. Navy Austin-class dock landing ship USS Juneau (LPD-10) sank to the seabed over 200 nautical miles off the coast of the Mariana Islands training area. The final blow was delivered by a torpedo launched from a Japan Maritime Self-Defense Force submarine. According to Defense News and the U.S. military's DVIDS, this SINKEX (sinking exercise with a real ship as a target) was conducted as part of Valiant Shield 26.

More Important than the Sunk Ship is the Launching Side

Juneau, which was commissioned in 1969 and participated in the Vietnam War and the Gulf War, was an outdated vessel that was decommissioned in 2008. While it was suitable as a target ship, the key point this time is not the ship's age. It is significant that the JMSDF submarine undertook a torpedo attack against a real ship within a multilateral integrated operation. The name of the launching submarine, the type of torpedo, and the firing conditions have not been disclosed. This undisclosed information indicates the boundary between the capabilities the JMSDF wanted to showcase and those it preferred to keep hidden.

Positioning of Valiant Shield 26

According to the U.S. Pacific Fleet, Valiant Shield 26 was conducted from June 22 to July 1 in the Northern Mariana Islands, Guam, Japan, and surrounding waters. The participating countries included the United States, Japan, Australia, Canada, and New Zealand, marking the 11th iteration of the exercise that began in 2006. From 2024 onward, the exercise is expected to transition to a more clearly defined multilateral and integrated exercise, and this was considered the second opportunity where the Self-Defense Forces were deeply involved in planning and execution.

Rear Admiral Eric Anduze, commander of the 5th Carrier Strike Group and Task Force 70, stated that the SINKEX was "an opportunity to hone the precise lethality and coordination capabilities essential for advanced maritime operations in the Pacific theater."

Live Fire Verification of Surface Warfare, Not Anti-Submarine Warfare

The scenario of a submarine sinking a surface ship with a torpedo evokes memories of Cold War maritime blockades. However, this training was not a simple reenactment of submarine versus ship. DVIDS explained that air, surface, and underwater forces coordinated to attack the target. In other words, the JMSDF submarine was not searching for prey alone but was part of an integrated chain of detection, tracking, target allocation, and engagement.

This connects to the defense of the southwestern islands. The issues around the first island chain involve not only the stealth of submarines but also the speed at which friendly aircraft, patrol aircraft, surface vessels, and space/cyber information can be connected. The JMSDF has maintained a high standard of P-1 patrol aircraft, escort ships, and submarines, but the experience of being entrusted with the final strike in a multilateral operation is different from routine joint training.

The Weight of History with USS Juneau

Defense News pointed out that the name USS Juneau recalls the light cruiser Juneau (CL-52), which sank in November 1942 due to a torpedo from the Japanese submarine I-26 during the Battle of Guadalcanal. This time, it was a training exercise with allies, and there is no need to overly inflate historical comparisons. However, the fact that the U.S. Navy used a decommissioned ship bearing that name for training to be sunk by a JMSDF submarine's torpedo indicates a significant change in the psychological distance of the Japan-U.S. alliance.

Remaining Challenges: Ammunition and Political Decisions

In my view, the outcome of this exercise does not prove that "Japan can sink enemy ships." This is not a new discovery for the JMSDF. Rather, it is significant that Japan's underwater combat capabilities can be confirmed to be responsible for actual lethality within the U.S. military's integrated firepower system.

However, there is a quiet risk here. Live-fire SINKEX exercises are expensive and require target ships, maritime areas, environmental management, and coordination among countries. Even if a few successes occur during peacetime, without the ability to sustain ammunition stockpiles, maintenance capabilities, and information-sharing speed in times of crisis, these capabilities will remain a one-time symbol. The true weakness of Japan-U.S. ASW may lie not in the performance of submarines but in the political decisions that allow engagement and the speed of resupply.