On 31 July 1941, the Japanese invaded French Indochina, where they seized "Pégase", which was returning from a mission. Concerned about a possible Japanese attack on Madagascar, which would compromise the security of the supply lines to India, the British led an attack on Diego-Suarez, the principal French base, beginning on 5 May 1942. During the attack, three "Redoutable"-class submarines were sunk: "Bévéziers", and "Le Héros" by Fairey Swordfish and "Monge" by destroyers. "Monge", after having launched one torpedo at the , was spotted, fired upon by three destroyers and sunk.