The submarine continued to take a heavy toll on shipping on her fourth war patrol, and on the night of 6–7 February 1943, she approached a convoy stealthily for a surface attack. Suddenly a convoy escort named "Hayasaki" closed and prepared to ram. As the small ship charged out of the darkness, Gilmore sounded the collision alarm and shouted, "Left full rudder!" — to no avail. Perhaps inadvertently, hit the Japanese adversary amidships at 17 knots (31 km/h), heeling the submarine 50 degrees, bending 18 feet of her bow sideways to port, and disabling the forward torpedo tubes.