 In the early hours of May 19 , PC @-@ 815 's sonar detected what the crew believed to be an enemy submarine off Cape Lookout , about ten to twelve miles offshore . Over the next two and a half days , Hubbard ordered his crew to fire a total of 35 depth charges and a number of gun rounds to target what Hubbard believed to be two Imperial Japanese Navy submarines . The PC @-@ 815 was joined by the US Navy blimps K @-@ 39 and K @-@ 33 , the US Coast Guard patrol boats Bonham and <unk> and the subchasers USS SC @-@ 536 and USS SC @-@ 537 to assist it in the search for the suspected enemy vessels . Hubbard was given temporary command of the vessels on the afternoon of May 19 . The larger subchaser PC @-@ 778 also joined the submarine search , though it found no indication of submarines and its commander was subsequently castigated by Hubbard for his refusal to lay its own larger stock of depth charges or resupply the PC @-@ 815 . 
