On Iwo Jima, McCarthy was the company commander of G Co. 2nd Battalion 24th Marines. He landed on yellow beach 2 alongside the 23rd Marines. On D plus 3, the 24th RCT relieved the 25th.
During the Iwo Jima campaign, McCarthy was a key figure in the 24th Marine Regiment. He led G Company during the landing on Yellow Beach 2 and played a role in relieving the 25th Marines on D plus 3.