In July 1943 O'Daniel landed in Sicily (Operation Husky) with the 3rd Infantry Division. On July 24, 1943, two weeks after the initial landings, he returned to Algiers and was attached to the 36th Infantry Division, another National Guard formation, recruiting from Texas, under the command of Major General Fred L. Walker, for the Salerno landings (Operation Avalanche) in September. Although not required to do so, he chose to land with the troops at Salerno. He became officer in charge of amphibious operations for the Fifth Army on October 1, 1943 and the following month was reassigned as the assistant division commander (ADC) of the 3rd Infantry Division, commanded by Major General Lucian Truscott. The division crossed the Volturno Line and advanced up the spine of Italy until being held up by the formidable German Winter Line (also known as the Gustav Line) defenses. The division, after spearheading the Fifth Army's advance and had seen much hard fighting and heavy casualties, was withdrawn for rest in November.