When WWII broke the United States had no mechanized flamethrowing capability. It is believed that an officer in the 754th U.S. Army tank battalion came up with the idea of mounting a flame thrower on a M3 Light tank on the island of New Caledonia. The Army used the idea on New Georgia and the Marines during the Battle of Bougainville. After which further development passed to the U.S. Army. Chemical Warfare Service at Schofield Barracks, Territory of Hawaii. There the Army reached out to the United States Naval Construction Force for assistance. The Seabees accepted the offer and converted or modified nearly 400 tanks for the Army. Those weapons set the standard for the U.S. through the Korean War. It was not until 1955 that a superior flame throwing tank replaced the Shermans the Seabees created.
World War II
During WWII Seabees of the 117th U.S. Naval Construction Battalion modified/created the main armament flame throwing tanks that were used in the Pacific theater by the USMC in the battles of Saipan, Tinian, and Iwo Jima and the U.S. Army on Okinawa. They were a weapon Japanese troops feared and the Marine Corps said was the best weapon they had in the taking of Iwo Jima. After Okinawa the Army stated that the tanks had a psychological presence on the battlefield. U.S. troops preferred to follow them over standard armor for the fear they put in the enemy. The U.S. Army credits them with saving American lives.
Pacific field commanders had tried field modified mechanized flame throwers early on, with the Marine Corps deciding to leave further development to the Army. The Navy had an interest in flame throwing and five Navy Mark I flamethrowers arrived in Hawaii in April 1944. The Navy deemed them "unsuitable" due to their weight and turned them over to the Army's Chemical Warfare Service. In May a top secret composite unit was assembled at Schofield Barracks. It was led by Colonel Unmacht of the US Army Chemical Warfare Service, Central Pacific Area (CENPAC) Col. Unmacht began the project with only the 43rd Chemical Laboratory Company. They modified the first light tank designating it a "Satan". The flame tank group was expanded with men from the 5th Marine tank battalion and 25 from the 117th CB. The newly attached Seabees went over what the Army had created and concluded it was a little over engineered. They recommended reducing the number of moving parts from over a hundred to a half dozen.