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The Oil Slick In

Blackett Strait

The USS Grampus completed training exercises off Brisbane on 12 February 1943. She bid farewell to her practice ship and headed north for her sixth and final patrol. Her orders were to patrol south of New Britain. She was never heard from again. In most accounts two possible causes for her loss are discussed albeit with the caveat her loss remains an unsolved mystery. One of the causes has always seemed very unlikely to me based on the facts. Nevertheless it seems to be the accepted cause for the Grampus’s loss for many World War II submarine veterans. Its backstory began on 2 March 1943. The Grampus and the USS Grayback were ordered to move to the Vella Gulf and be on guard for enemy ships escaping from Vila on Kolombangara, which was to be bombarded by warships of a U. S. Navy task force on March 6th. There is no proof the Grampus ever received these orders, because she was not heard from after February 12th. On the night of March 5th the IJN destroyers Murasame and Minegumo delivered supplies to the Japanese garrison at Vila. As they withdrew after landing their cargo, they encountered Rear Admiral Aaron S. Merrill’s task force of cruisers and destroyers in the Kula Gulf and were sunk. Also on March 5th, at 2155 hours, the Grayback had a sonar and visual contact in the Vella Gulf on a distant ship, which her captain assumed was the Grampus; he maneuvered to avoid it. The Grayback’s patrol report states “Kept clear assuming this to be Grampus as it was sighted in area assigned to her.” On March 6th, a large oil slick was reported in Blackett Strait. This report together with the Grayback’s contact fueled speculation that the Grampus may have been sunk as a result of an encounter with the two IJN destroyers before they were sunk by the U. S. Navy task force. And because the Grayback did not hear any depth charges, it was also speculated the Grampus must have been caught on the surface and destroyed by battery fire from the two destroyers.

There is no pedigree for the report of the large oil slick. It is unknown who made the report or the position where the slick was sighted (other than “in the Blackett Strait”). Fifty-three survivors from the Murasame and 122 survivors from the Minegumo managed to return to Japanese lines. Two other survivors from Minegumo were captured by American forces. No reports were received from the destroyers or their survivors about antisubmarine activity. If there was an action against an American submarine in Blackett Strait the survivors would have reported it. I believe that the most likely cause for the Grampus’s loss is an attack by Japanese naval aircraft on 19 February 1943 off New Britain against the submarine which had attacked and damaged the transport and aircraft ferry Keiyo Maru. That submarine was the Grampus.

USS Grampus

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