At 2120 on the evening of 13 July, a patrol plane sighted a Japanese
submarine submerging some 78 miles from Rorpgattan Point, Saipan, and reported the enemy's position. Accordingly,
William C. Miller and the other members of a hunter-killer group – carrying the officer in tactical command (OTC) – altered course and departed the screen for the transport area to track the submersible. At 0022 on the following day, the destroyer escort and her sisters arrived on the scene and commenced searching. Seven hours later,
William C. Miller obtained
sound contact at a range of . The destroyer escort approached at 15 knots and dropped a 13-charge pattern at 0726. Opening the range after observing no damage, the escort vessel attacked for the second time, dropping a second pattern at 0752, once again, of 13 charges. That pattern appears to have proved devastating to . At 0804,
William C. Miller noted pieces of wood popping to the surface about ahead, one point on the
starboard bow. One minute later, a "heavy and prolonged underwater explosion" – estimated to be about three times the shock of a
depth charge explosion – shook the ship. Shortly thereafter, observers in
William C. Miller noted a large "boil" in the water some in diameter. At 0806, the destroyer escort laid a third 13-charge pattern that apparently landed atop the submarine, completing whatever devastation had been wreaked by the second salvo.
William C. Miller closed the oil slick and debris and lowered a boat to investigate. The ship soon recovered small pieces of cork insulating material; fractured wooden decking; and a fur-lined, Japanese seaman's cap. The depth charge barrage had literally torn the submarine apart. A postwar accounting credited
William C. Miller with the destruction of the Japanese submarine
I-6. The Navy, in what seems to be in error gave credit to William C. Miller for sinking the I-6, but due to recent research information presented by "combinedfleet.com", it seems to have been the I-55. I-6 was sunk in a collision with the freighter TOYOKAWA MARU on 16 June 1944 ==Continued convoy and anti-submarine operations==