 However, at , "RO-501" ran into a U.S. Navy hunter-killer group comprising escort carrier and five destroyer escorts, including .The group's presence forced "RO-501" underwater for two days, during which her batteries were depleted and her captain radioed a coded signal that he was being pursued.Unfortunately, this transmission was detected by the American ships with their high-frequency direction finding ("Huff-Duff") equipment, which enabled them to pinpoint the submarine's location.