USS Dorado (SS 248) (LtCmdr E.C. Schneider, USN) went missing on her maiden voyage between New London and the Canal Zone. After her scheduled date of arrival on 14 October 1943, air searches were begun, but they only found widely scattered oil slicks and debris.

The loss of USS Dorado (SS 248) is usually attributed to an attack of the US Mariner aircraft (VP-210 USN/P-9, pilot Lt(jg) Daniel T. Felix, Jr.) stationed on NAS Guantanamo Bay, Cuba on 12 October 1943. The aircraft was patrolling around convoy GAT-92 and dropped three depth charges and one bomb on a surfaced U-boat at 20.51 hours on 12 October. But no explosion was observed and no oil or debris was seen when the plane circled the diving area. During the same patrol the Mariner sighted at 22.33 hours another U-boat not far from the first attack position. They knew that an American submarine was in the vicinity and tried to exchange recognition signals after dropping flares. But the U-boat immediately opened fire with the AA gun, forcing the aircraft to evade, which lost contact with the crash diving U-boat before any attack could be made. Both attacks can be found in the KTB of U-214 with the German times 01.47 and 03.30 hours on 13 October 1943. In the first attack in grid EC 54 four bombs were dropped which were apparently duds. In the second attack in grid EC 52 they mention that an illuminated aircraft attack was fought off with the AA gun. The times and descriptions of both attacks fit to the attacks reported by the pilot of the Mariner.

Between 15.51 hours on 19.02 hours on 8 October 1943, U-214 had laid a mine field of 15 mines in the approaches off Colon, Canal Zone. It is possible that USS Dorado (SS 248) was lost on one of these mines when she passed the area on her way to the submarine base at Coco Solo on 14 October. The mine field was detected on 16 October and ten mines swept.