At 0555 on the morning of 24 July 1943, Lieutenant Commander L.R. “Dan” Daspit, the commanding officer of USS TINOSA (SS-283), spotted the Japanese fleet’s largest tanker as it headed straight for his sub. Tonan Maru No. 3 weighed over 19,000 tons and was making her way from Palau to Truk with a cargo of precious fuel; TINOSA had been alerted to the ship’s movements by codebreakers and was ready to act. At 0928, TINOSA fired four torpedoes, two of which struck the target and exploded. “Two explosions heard by personnel in submarine,” Daspit wrote in his patrol report. “Second hit in port quarter made much smoke and target stopped, took port list and settled by stern almost immediately.” Figuring Tonan Maru No. 3 was on the ropes, Daspit moved in for the kill. “Having observed target carefully and found no evidence of sinking, approached and fired one torpedo at starboard side,” he wrote. “Hit, heard by sound to stop at same time I observed large splash. No apparent effect. Target had corrected list and was firing at periscope and at torpedo wakes with machine guns and four inch.” By this point, TINOSA had expended seven torpedoes on the tanker with only two explosions. At 1011, she tried again. “Fired eighth torpedo. Hit. No apparent effect.” The same phrase applied to torpedoes nine and ten. At 1048, “fired eleventh torpedo. Hit. No effect. This torpedo hit well aft on the port side, made a splash at the side of the ship, and was then observed to have taken a right turn and to jump clear of the water about one hundred feet from the stern of the tanker. I find it hard to convince myself that I saw this.”
One can imagine Daspit’s mood as he launched torpedoes twelve, thirteen, fourteen, and fifteen, all of which hit but failed to explode. By 1130 a Japanese destroyer had arrived on scene and begun depth charging. Daspit chose not to retaliate: “Had already decided to retain one torpedo for examination by base.” Instead, he took TINOSA deep and the destroyer passed overhead: “Screws could be heard clearly through the hull at 310 feet.” At 1357, the sub eased back to the surface to find the tanker still afloat. Four hours later, Daspit reported to COMSUBPAC and asked that another sub be dispatched to destroy the tanker. At 2220, the order came to return to Pearl Harbor.
The journey back did not provide Daspit with enough time to cool down. When TINOSA arrived, he set out for SUBPAC’s office. Rear Admiral Charles Lockwood, COMSUBPAC, described what happened next. “I expected a torrent of cusswords, damning me, the Bureau of Ordnance, the Newport Torpedo Station and the Base Torpedo Shop, and I couldn’t have blamed him—19,000 ton tankers don’t grow on trees. I think Dan was so furious as to be practically speechless. His tale was almost unbelievable, but the evidence was undeniable.” An inspection showed nothing wrong with the torpedoes, but after Commander Swede Momsen actually fired three of them at a Hawaiian cliff and only two exploded, the cause became more apparent. The torpedoes were equipped with firing pins that were positioned in such a way that if a ship were hit straight on, at a 90-degree angle, the pin’s spring could not move quickly enough to trigger an explosion. TINOSA’s first two torpedoes worked because they had struck glancing blows—the less-optimal angles had yielded the desired results.
The Navy immediately set to work on a solution, but long before one was discovered TINOSA was back at sea. She would go on to complete a total of twelve war patrols, receiving nine battle stars and Presidential Unit Citations for her fourth, fifth, and sixth patrols.