October 14, 1943 – USS Dorado failed to arrive at the Panama Canal Zone, and aircraft were launched to search, without success, for the submarine. Early suggestions that she was sunk in error by a US Mariner aircraft was later concluded as incorrect, and it seemed likely that her loss was attributable to an unknown accident on board or to a German naval mine. USS Dorado (SS-248), a Gato-class submarine, was the first submarine of the United States Navy to be named for the dorado, also known as the dolphinfish or mahi-mahi. Her keel was laid down on 27 August 1942 by the Electric Boat Company of Groton, Connecticut. She was launched on 23 May 1943 (sponsored by Mrs. Ezra G. Allen), and commissioned on 28 August 1943, Lieutenant Commander Earle Caffrey Schneider in command. Dorado’s sea trials proved the readiness of the crew, and she sailed from New London, Connecticut, on 6 October 1943 for the Panama Canal Zone. She did not arrive. The standard practice of imposing bombing restrictions within an area 50 nmi (93 km) ahead, 100 nmi (190 km) astern, and 15 nmi (28 km) on each side of the scheduled position of an unescorted submarine making passage in friendly waters had been carried out and all concerned had been notified. However, the crew of a PBM Mariner of Patrol Squadron 210 out of Guantánamo Bay, Cuba, assigned to provide air coverage on the evening of 12 October had received an incorrect description of the restriction area, 11 nmi (20 km) out of place. At 2049 local time, under a moon-lit but stormy sky, that plane attacked an unidentified submarine that it believed was outside the restriction area with three Mark-47 depth charges and a 100 lb (45 kg) Mark-4 Mod-4 demolition bomb. About two hours later, the plane sighted a second submarine with which it attempted to exchange recognition signals. This second submarine fired upon the plane. A convoy scheduled to pass through the restricted area surrounding Dorado on the evening of 12 October reported no contact. Air searches were begun immediately after 14 October, her scheduled date of arrival. Widely scattered oil slicks with occasional debris were found. Subsequently the Board of Investigation held in Guantánamo Bay, and the more formal Naval Board of Inquiry held at the Washington Navy Yard, found that the “widely scattered oil slicks” were actually oleous in nature and not bunker oil or fuel – most probably rotting vegetation like seaweed. All of the “occasional debris” was determined not to have come from Dorado. At both the Board of Investigation and the Court of Inquiry, the aircrew testified that they were certain that both submarines they had attacked were U-boats. Despite the circumstantial evidence, there are reasons to doubt that Dorado was sunk by the Mariner. Because the crew knew that Dorado was operating in the area, they carefully observed their two targets before attacking. Prior to the first attack, the four crewmen of the aircraft observed the surfaced submarine for 12 minutes, noting: it was 48 nmi (89 km) from where they had been told to expect Dorado to be and 34 nmi (63 km) from where Dorado really was supposed to be: it was heading almost 90 degrees off from Dorado’s base course; it had no guns on the fore deck where Dorado carried a five-inch (127 mm) gun; it had an entirely grooved deck where Dorado’s deck was grooved only near the conning tower; it had a “knob-like” object on the front of the conning tower, almost certainly the Biscay Cross radar detector installed on Type IX U-boats Post-war examination of Kriegsmarine records indicate that the submarine first attacked by the Mariner may have been U-518, though that boat’s logs do not record the attack. It is possible that the attack went unnoticed by the boat; of the three depth charges and one 100 pound bomb that were dropped, one depth charge was a confirmed dud, one was dropped too low to arm, and neither the third depth charge nor the bomb were seen to explode. After the attack, the Mariner searched the area for 20 minutes, but saw no explosions, bubbles, or debris. The second submarine, attacked by the Mariner two hours later, was certainly U-214; her log book, captured after World War II, describes firing at the aircraft. On 8 October, five miles off Colón, U-214 laid a minefield of 15 mines. One of these may have sunk the United States Navy submarine USS Dorado (SS-248) on or about 14 October.