Australia (1943-45)

Infantry tank – 25 built

A need for Firepower

In early 1943, a General Staff specification was issued for a tank mounted flame projector for use by Australian units in the Pacific. Plans were submitted for a cordite based flamethrower designed by Major A.E Miller, the commanding officer of the Australian 2/9 Armoured Regiment Workshop, but no action was taken to develop the design. A separate Matilda II mounted design utilizing compressed air propellant was produced by the Munitions Supply Laboratory under the designation of ‘Flamethrower, Transportable Aust No. 1 Mk I’. The flamethrower was tested but with an unsatisfactory range of 14-19 yards (13-17 m). In November 1943, a panel including Major Miller was formed to investigate potential new designs for a tank based flame projector. On January 7, 1944, a new requirement was issued for a flamethrower mounted in the turret of a Matilda II infantry tank, with the design to be completed by February 7, 1944. The working design was a cordite based flame projector refined from Major Miller’s original design, however, it required fabrication of components which would extend completion past the deadline.

Major Miller proposed an alternative design based on a hydro-pneumatic cylinder which could be fabricated from available components and was approved, with a budget of 250 pounds. The new system utilized an electrically powered hydro-pneumatic piston to generate pressure for the flame projector and a prototype designated ‘Frog’ was completed on February 21, 1944. The prototype Frog was tested on April 2, and a refined system was approved for production of 25 units. Major Miller was transferred to the Master General of Ordnance (MGO) branch to oversee design and production. The first tank was delivered by July 22, 1944, and successfully demonstrated to the Commander of the Australian Military Forces, General Thomas Blamey, at Monegeetta Proving Grounds on July 26. The production flame tank was officially adopted under the name of ‘Flamethrower, Transportable Frog (Aust) No. 2 Mk I’, but is more commonly known as the ‘Matilda Frog.’

Diagram of the major components of the ‘Frog’ flame system. Source: The Australian War Memorial

Design and specifics

The flame projector on the Frog replaced the Matilda’s standard 2-Pounder (40 mm/1.57 in) main gun. The flame projector was encased in a mild steel tube designed to resemble the 3-inch close support howitzer, but fitted with a counter weight near the end of the barrel for balance. The hydraulic traverse of the regular gun tank was retained and a new hand cranked chain-sprocket mechanism was affixed to the turret roof to control elevation. The coaxial BESA machine gun was also retained although the bulk of the flame projector made loading and servicing the weapon in combat extremely difficult. The most novel feature of the flame projector was the electrically powered hydro-pneumatic cylinder which generated pressure for the weapon instead of the more conventional cordite or compressed gas.

The hydro-pneumatic cylinder was comprised of a floating piston contained within two nested steel cylinders. During operation, fuel was electrically pumped into the inner cylinder, pushing the piston down and triggering a limit switch. Simultaneously, the air in the outer cylinder was pressurized by the depression of the piston, charging the weapon to fire. At full retraction, the inner cylinder contained 10 gallons of fuel. Firing the weapon released a pintle valve, allowing the pressurized air in the outer cylinder to expand and force the piston upwards, thus discharging the stored fuel through the projector barrel. A foot trigger controlled the release of fuel from the pressure cylinder while a thumb switch on the traverse controller was responsible for triggering the electrical igniter located at the end of the barrel. Releasing the foot trigger or expenditure of the stored fuel activated the fuel pumps and re-primed the system.

Much of the commander and loader positions were replaced by the flame projector’s 80-gallon ‘Geletrol’ fuel tank and the hydro-pneumatic compressor system with the commander’s seat moved and affixed to the pressure cylinder. Geletrol was a locally produced thickened flame fuel produced by adding Aluminum Oleate to petrol, diesel or a petrol-diesel mixture (referred to as ‘Dieseline’). The decreased space in the turret meant that the Matilda Frog carried a crew of only three (driver, gunner and commander). Testing was conducted between August-November of 1944, however, tests were interrupted by the failure of the hoses connecting the hydro-pneumatic cylinder to the flame gun. Metal pipes articulated by ball joints were designed to replace the rubber hoses. Development proved difficult and this upgrade was not satisfactorily implemented until 1945 when Frog tanks were refitted in the Pacific Theater, although it is not known how many tanks were refitted before the conclusion of the war.



Photo of the turret interior of a Matilda Frog, taken from the commander’s cupola facing forward. The fuel tank can be seen towards the front of the turret next to the gunner’s position, with the compressor piston behind it. The system of ball jointed pipes (painted white) normally connects the barrel of the flame projector to the fuel tank and compressor, however, in this instance, the projector barrel has been removed. Source: Batrac



A Matilda ‘Frog’ Flame tank of 1 Armoured Regiment attacking a Japanese bunker during operation OBOE 2. The anti-grenade mesh is visible on the rear deck. Balikpapan, Borneo. July 3, 1945. Source: Australian War Memorial