A Japanese Soryu submarine collided with a commercial vessel as it was surfacing on Monday in the Pacific Ocean.
It's still unclear what caused the accident as there were no reported sonar and periscope issues prior to the collision, outlined Kyodo News, which happened at approximately 10:55 AM local time off Cape Ashizuri in Kochi Prefecture, Japan.
The Japan Maritime Self Defense Force's Soryu submarine was carrying out routine training when it inadvertently hit the commercial ship Ocean Artemis, a cargo vessel registered in Hong Kong transporting iron ore, as it was surfacing.
Ocean Artemis spans a hefty 228 meters (750 feet) long, and weighs some 51,000 tons — so it's tough to imagine such a ship going unnoticed. By comparison, the diesel-electric Soryu submarine has a standard displacement of 2,950 tons and is just over 83 meters (275 feet) long.
🇯🇵 Japanese submarine Soryu (largest conventional submarine in the world) suffered minor damage after collision with merchant ship while training off coast of Japan.— Navy Lookout (@NavyLookout) February 8, 2021
3 submariners suffered minor injuries.https://t.co/PxwNy4CGFJ pic.twitter.com/tmsId5VOMJ
The 5th Regional Coast Guard Headquarter in Japan is carrying out an investigation to uncover exactly what went wrong, and why, as well as sending its divers to check the cargo ship's hull wasn't badly damaged.
During the collision, the Soryu submarine suffered damage to its communications equipment, and fairwater planes — the wing-looking structures on its top tower.
Why such a collision could happen
The Coast Guard will be checking that proper surfacing procedures were carried out by the Soryu submarine's crew. Typically, sonar is used to detect other vessels in the vicinity, however, this can become trickier when the vessel is behind a submarine.
To ensure no collisions occur during surfacing, a submarine typically changes its position as it gradually rises to the surface, once near it, it then extends its periscope to look out for such vessels.
Some sources say, Kyodo News reported, that the Soryu's crew didn't detect the vessel through its sonar, and once it finally did, thanks to its periscope, it was unable to shift gear to move out of the way, and ended up scraping the hull of the ship. Other factors may have come into play, such as tidal currents, which can make using sonar trickier.
As investigations carry on, the real reason for the collision will be uncovered.