This is an official history study from the Marines in the Vietnam War Commemorative Series. This commemorative volume is an overview of Marine helicopters in the Vietnam War. Owing to Marine task organization and doctrine, rotary-wing aircraft were present in the Republic of Vietnam (RVN) from the start of Marine Corps involvement in the country.1 This book's purpose is to highlight pivotal moments during more than a decade of operations. Most of these occurred in the I Corps Tactical Zone. Both a political and military region in the northernmost section of the Republic of Vietnam, it was composed of five provinces: Quang Tri, Thua Thien, Quang Nam, Quang Tin, and Quang Ngai.2 This work presents the challenges, turning points, and issues that developed a rotary-wing capability into an invaluable asset for Marine ground operations.