"All Hands on Deck"

The Sinking of the 

Kensho Maru

Text & Photos by Mike Gerken

(Was to be published in "Wreck Diving Magazine" in 2019)

  Engine Room of the Kensho Maru                  The Japanese Imperial Navy lost an astonishing amount of shipping during WWII. A total of 9,700,000 tons with over 3000 merchant and naval vessels reported destroyed (See table A below). One of the highest concentrations of ships sunk during the war was in Truk Lagoon. On February 17-18, 1944 a US carrier-based air raid titled, “Operation Hailstone” laid waste to more than three-dozen Japanese merchant and military vessels sitting at anchor creating one of the most historic collections of WWII wrecks in the world.

                  Anyone who has ever dived the wrecks of Truk will easily spy gaping holes breeching the hulls of the ships. Massive chinks in the armor created by strafing planes dropping aerial bombs and slamming torpedoes into the hulls. In other words, it doesn’t take a wreck detective to figure out what caused some of these vessels to find their way to the bottom. However, there are a few wrecks where the details of their sinking are not apparent due to the lack of visible damage. The Kensho Maru is one such wreck.


                  The 383’ Kensho Maru was towed to Truk Lagoon by the Momokawa Maru and arrived on Jan 6, 1944 about 31 days prior to “Operation Hailstone”. It is believed that the damage visible today to the steerage mechanism may have been the reason to necessitate her towing to Truk. The wounded ship was brought to the repair anchorage and can be seen in the archival images (See below). The Kensho is in the vicinity of the Kiyosumi, Hoyo and Tonan Maru’s; all sunk during the raid. 

Repair Anchorage Repair Anchorage


                  With shallow depths of about 110' and the intact condition of the wreck make the Kensho a popular dive in Truk. The cathedral-like appearance of the upper engine room and the winding multi-level structure sharpens divers’ senses and contains fascinating engineering artifacts within. But how did the Kensho sink? What were the final hours like on board for the crew? While diving through the engine room I envision chaos unfolding as the they desperately tried to save their ship with the threat of explosions detonating all around them.


  US Planes Over TrukUS Planes Over TrukUS Planes over Truk Lagoon during Operation Hailstone February 17-18, 1944.                  On Feb 17, 1944 waves of US Dauntless dive bombers and Avenger torpedo planes attacked the repair anchorage approaching from the southeast. The Kiyosumi Maru was struck with two torpedoes on the starboard side and hit with at least one aerial-bomb amidships (see below). The last known image of the Kiyo shows her low in the bow with a geyser of steam and smoke launching hundreds of feet in the air. Only 400 feet away, the fleet oiler Hoyo Maru shows signs of her own fight for life. The ship is rolling heavy to starboard and low in the stern after being hit with several torpedoes, one in the stern.



The Kiyosumi Maru (foreground) and the Hoyo Maru (background) being attacked and sunk nearby the Kensho Maru.

                  The next archival image below shows no signs of smoke or fire emanating from the nearby Kensho Maru that would indicate a direct hit on the ship. The photo does show signs the Kensho was riding low in the stern and high in the bow with a slick of oil trailing behind her. This could indicate that the ship was flooding in the aft sections. U.S. action reports claim that the Kensho was hit several times but reported not sinking upon departure. Could these claims have been confused with direct hits to the Hoyo, Tonan and Kiyosumi Maru which where anchored nearby? In addition, the Yamagiri Maru was sunk only 1.5nm to the northeast with identical wounds the Kiyosumi suffered. The chaos in the repair anchorage would have been considerably elevated during the raid, potentially making reports inaccurate. The massive explosions nearby could have caused concussions strong enough to impair the water tight integrity of the Kensho’s hull. 

Kensho Maru center with oil slick astern but no smoke.

Inspection of the Kensho

                  The Kensho Maru today sits upright with an estimated 20-degree list to port. There is no evidence of serious damage to the outer hull below the waterline. The foredeck does shows signs of sagging but this could be simply from wear on the ship after 75 years on the lagoon seabed. Besides, the aerials photos of the Kensho show her riding low in the stern and not the bow. In addition, the superstructure and engine room are remarkably intact. Could the damage be hidden from view below the sand line?

The Engine Room The control area of the engine room. Note the floor plates moved or missing.

                  Exploring the engine room you will find some of the heavy steel floor plates were lifted and dropped into the bilge. I suspect the engine room was taking on water and the crew moved the floor plates to try to discover the source of the flooding and attempt to make repairs. At the aft section of the engine room there is a hose roughly 8 inches in diameter with an intake pick-up lowered into the deepest part of the bilge below the level of the floor (see below). Follow the hose up and it snakes out through a roughly hewn cutout in the steel watertight bulkhead that separates the engine room from cargo hold number four.  At the end of the hose topside is a standard quick release coupling which would have connected to a portable bilge pump either on deck or on the deck of a salvage vessel. This is a clear sign that lengthy salvage operations were attempted and that the vessel went down slowly.

The BilgePick-up below the floor in the bilge. Center is the pick up of the bilge pump hose. The floor plate removed for access.

                  On the deck behind the superstructure there are remains of O2 and acetylene tanks with cutting torches; more signs of hasty salvage work taking place. Why did the crew cut an access hole in a watertight bulkhead? Probably due to the hose being too short and unable to reach the lower engine room without it.


                  It goes without saying that a ship taking on water will founder if the capacity of the bilge pumps is less than the amount of water entering the ship. Despite the salvage efforts the Kensho Maru was doomed for this reason. The pumps just couldn’t keep up.

                  If the Kensho was to theoretically be lifted from the silt, I do not believe one would find a catastrophic breech in the hull. The type of salvage work taking place would not likely have been possible if the ship was in danger of rapidly sinking. The absence of fire & smoke emanating from the Kensho in the existing photos is another clue the ship was not grievously wounded. The surface slick seen in the one photo could have been the oily waste being pumped over board from the flooding engine room; a slick that was missing from the early image of the repair anchorage (at very top).  

                  In the overall scheme of war, the fate of one mid-sized cargo ship may seem insignificant to most but as a wreck diver and a captain myself I imagine the struggles the crew endured to preserve their ship. In this case, their efforts were futile but I'm sure valiant all the same. This was an “all-hand’s-on-deck” emergency; a situation I hope to never have to experience myself.

Michael Gerken is a dive travel tour leader, professional underwater photographer, documentary filmmaker, photo journalist and captain of the M/V Odyssey in Truk Lagoon. Follow Mike’s work at www.evolutionunderwater.com or on Facebook https://www.facebook.com/Mike.Gerken100 or email [email protected].

Join Mike in Truk on board the M/V Odyssey. 

Reference Materials

“The WWII Wrecks of the Truk Lagoon” author Dan Bailey

Archival Images Courtesy of the National Archives & Records Administration


Table A

Table AJapanese Tonnage Lost WWII