She was placed in full commission 20 April and assigned to Inshore Patrol Squadron, 5th Naval District, based at Norfolk, Virginia.

During one period of this duty, 24 December 1942 to 13 June 1943, Plymouth completed eight convoy escort voyages from New York to Key West and back.

At 21.37 hours the following evening she made underwater sound contact about 90 miles east of Elizabeth City, North Carolina.

Lieutenant Ormsby M. Mitchel, Jr., USNR, in command of Plymouth, was thrown violently against a bulkhead and sustained serious injuries, which later required amputation of his left leg.

Rescued from a raft by USCGC Calypso, Lieutenant Mitchel was awarded the Navy Cross for extraordinary heroism.

Ensign Rubin Keltch, of New York City, was also awarded the Navy Cross posthumously for his service aboard the Plymouth.