sentences:  Training at Guantanamo Bay and Bermuda preceded the next patrol, from 23 January 1945 to 7 February, during which her task group formed a part of the escort for , carrying President Franklin D. Roosevelt toward the Yalta Conference.Additional training in Narragansett Bay and Casco Bay prepared her for her final antisubmarine patrol, during which she won the Presidential Unit Citation, for her high achievement in joining in sinking two submarines on the night of 15 – 16 April.The first contact was made by just before midnight, and "Frost" joined in the attack which produced a violent underwater explosion at 0114 on 16 April.