On 8 April, after the fast carriers of TF 77 sailed south to Formosa to counter a perceived threat there, "Bataan" and HMS "Theseus" replaced them in the Sea of Japan. The two light carriers, screened by a pair of American destroyers and four British Commonwealth escorts, maintained the west coast blockade. Corsairs from Marine Attack Squadron VMF-312 along with British Fairey Firefly and Hawker Sea Fury fighters, bombed and strafed communist supply routes near Wonsan, Hamhung, and Songjin. Five aircraft and one pilot were lost to communist antiaircraft defenses.