After a shakedown cruise in the eastern Atlantic, "Nicholson" escorted convoys through the U-boat-infested North Atlantic first from Boston to Newfoundland and then to Scotland and England until fall 1942. In a brief training period off the Virginia coast, she prepared for the Casablanca invasion, but a turbine casualty prevented her participation in the initial landings. She arrived four days later, 12 November, to assist in the consolidation of the beachhead and to patrol. She took part in the Bizerte campaign and the initial assaults on Salerno, coming under heavy air attack from the Luftwaffe at both Bizerte and Salerno.