Mount Olympus departed from the East Coast in early July, arriving at Hawaii via the Panama Canal on 23 July. With the Commander, 3rd Amphibious Force, embarked, she was underway from Hawaii on 29 August. She arrived Leyte Gulf 20 October, there to serve as the floating headquarters for the huge U.S. Army invasion force. The landing force was subjected to continual air attacks, but its survival was assured by the American naval victory in the Battle of Leyte Gulf, which destroyed the Japanese Navy as an effective combat force.