United States Naval Construction Battalion flame thrower tanks

During the crucible of World War II, the United States Naval Construction Battalions, colloquially known as the Seabees, emerged as pivotal figures in the development and deployment of mechanized flamethrowers. Far from their traditional roles of building infrastructure, these highly adaptable engineers were instrumental in modifying and creating the primary flame thrower tanks that saw extensive service in the Pacific Theater. These formidable machines were not merely weapons; they were instruments of psychological warfare, instilling deep-seated fear in Japanese forces.

The U.S. Marine Corps, in particular, lauded these tanks as indispensable assets during the brutal campaigns for Saipan, Tinian, and Iwo Jima. The U.S. Army, too, recognized their profound psychological presence on the battlefield, noting that troops often preferred to advance behind these fiery behemoths rather than standard armored vehicles.

This preference underscored the tanks' dual role: a physical threat and a potent morale weapon, significantly influencing battlefield dynamics and enemy resolve.

The genesis of these specialized tanks involved a collaborative, albeit sometimes improvisational, effort. Early attempts by field commanders to integrate flamethrowers into armored vehicles proved challenging. The Navy's initial acquisition of five Mark I flamethrowers, deemed too heavy and cumbersome, were ultimately transferred to the Army's Chemical Warfare Service.

It was at Schofield Barracks that a top-secret project, led by Colonel Unmacht, began. Initially comprising the 43rd Chemical Laboratory Company, the unit was soon augmented by Seabees from the 117th Construction Battalion and elements of the 5th Marine tank battalion. The Seabees' practical, no-nonsense approach quickly identified that the initial Army design was 'over engineered.' Their recommendation to drastically reduce the number of moving parts, from over a hundred to a mere half-dozen, was a testament to their engineering acumen and focus on battlefield reliability.

This led to the creation of the 'Satan' tank, a light tank modified to carry a flamethrower with a range of 40-80 yards, marking a significant departure from traditional tank armament.

The demand for more potent and longer-range flamethrowers led to the conversion of the ubiquitous M4A3 Sherman medium tanks. Under Colonel Unmacht's direction, Seabees integrated the best features from various flamethrower units, including the Canadian Ronson, Navy Mark I, and other Navy-derived systems. The result was the CB-H1 (Construction Battalion-Hawaii 1), a powerful flamethrower operating at 300 psi, capable of projecting its incendiary stream up to 400 feet with a 270-degree traverse.

This was quickly superseded by the even more effective CB-H2. The development of these systems was a monumental undertaking, requiring extensive welding, electrical work, and significant financial investment per tank. Crucially, the Seabees also oversaw the development and mass production of stabilized flamethrower fuel, napalm, producing over 250,000 gallons.

This fuel was vital for sustaining prolonged fire attacks, as evidenced by the 713th Tank Battalion's consumption of 200,000 gallons during the Battle of Okinawa alone.

The strategic deployment of these flame thrower tanks had a profound impact on the Pacific campaigns. During the Battle of Iwo Jima, the limited number of these tanks meant they were pooled and dispatched as needed, often becoming the bottleneck for Marine assaults. The effectiveness of the flame tanks was so pronounced that casualty rates for portable flamethrower units soared, leading to an increased reliance on their mechanized counterparts.

The tanks' ability to neutralize fortified positions and bunkers, often impervious to conventional tank fire, was invaluable. The development and production of these tanks received 'Triple A' procurement priority, placing them on par with the B-29 bomber and atomic bomb projects, highlighting their critical importance. By Victory over Japan Day, Colonel Unmacht's Flame Tank Group had produced a total of 354 tanks.

The legacy of these Seabee-engineered infernos extended beyond World War II, with modified Shermans forming the 'Flame Dragons' unit in the Korean War, underscoring their continued relevance in mechanized warfare.