The destroyer escort arrived in New York on 17 March for a five days of voyage repairs, after which she returned to planeguard duty for "Card". On 14 April, "Bostwick"s escort division received orders to search for a submarine just outside the mouth of the Chesapeake Bay. The division split into northern and southern groups to scout the sea lanes. On 29 April, the northern group made contact with a submarine when sighted the snorkel of a U-boat. "Bostwick", "Thomas", and joined Natchez in dropping depth charges until heavy debris, a large oil slick, and a huge underwater explosion indicated the destruction of .