Collisions between submarines and surface vessels are fairly common. The U.S. Navy has seen nearly 50 collisions between surface vessels and submarines since 1983. In 2009, the Los Angeles class Attack Submarine San Francisco even managed to collide with an entire submerged mountain at 25 knots. In virtually all cases involving a submerged submarine running into another vessel, the submarine is generally found to be at fault. Under the rules of maritime navigation, a submarine below the surface is considered the “burdened” vessel, and the surface ship the “privileged vessel” in terms of the Right of Way. A submerged sub is not visible visually or on the radar which blinds the surface vessel to its presence and intentions. This means that the submarine’s crew has the responsibility to avoid colliding with the “privileged” vessel.

Before any submerged sub surfaces, there is a series of procedures it must follow to ensure that no other vessels are near it. The normal precautions would include: not surfacing in the midst of well-traveled sea lanes leading into or out of a port; having a precise plot of any sonar contacts before surfacing; and finally stopping at periscope depth to have a 360-degree look at the surrounding waters before you surface. Reports indicate that the Ocean Artemis was visible in the telescope as the Soryu came to the surface, which suggests that the submarine did not have an accurate sonar plot of it prior to the event.

The loss of this submarine to extensive repair and overhaul could not come at a worse time for Japan’s fleet. Recently the Chinese Navy has begun cranking up the pressure on Japan in the East China Sea over possession of the Senkaku/Diaoyu Islands which both countries have laid claim to. China has maintained a near-continuous naval presence in the islands’ waters for the last 17 months. The Communist Chinese have in the last month authorized their Coast Guard to use gunfire against any vessel intruding on the area. At some point, this will bring an armed Chinese vessel and an armed Japanese vessel into conflict.

For the MSDF, submarines like the Soryu act as invisible picket boats watching and reporting on Chinese Communist naval activities in the waters near Japan. The loss of the Soryu for repairs will make that job harder.