After trial runs and crew training, "Underhill" moved to the Boston Navy Yard for provisioning and loading of ammunition. On 2 December 1943, she was underway to Bermuda for further training and shakedown, returning to Boston Navy Yard on 10 January 1944 for minor repairs. She got underway from Boston on 17 January 1944 and arrived at Guantanamo Bay on 22 January, reporting to Commander, Caribbean Sea Frontier, for duty. She operated out of Trinidad and Guantanamo escorting convoys until late in May when she escorted SS "George Washington" from Kingston, Jamaica, to Miami, Florida.