The Japanese remained unaware of the base's existence until their plans for expansion in south-east Asia had come to nothing, even during their carrier raids in the Indian Ocean in April 1942. Later in the war, submarine reconnaissance established the base's existence. Despite openings into the lagoon being permanently closed by anti-submarine nets, the torpedoed the tanker "British Loyalty" in March 1944 (she had been previously torpedoed and sunk at Diego Suarez); it was an impressive long-range shot from outside the atoll through a gap in the anti-torpedo nets. Although seriously damaged, the tanker did not sink. She was not fully repaired but kept as a Ministry of War Transport Oil Fuel Storage Vessel. There was significant oil pollution after this incident and British personnel were used to clean the lagoon.