(33 US gallons) per second, where they were ignited by a spinning electrical igniter. Thrust increased from 8 tons during this preliminary stage whilst the fuel was gravity-fed, before increasing to 25 tons as the turbopump pressurised the fuel, lifting the 13.5 ton rocket. Combustion gases exited the chamber at , and a speed of 2000 m (6500 feet) per second. The oxygen to fuel mixture was 1.0:0.85 at 25 tons of thrust, but as ambient pressure decreased with flight altitude, thrust increased until it reached 29 tons. The turbopump assembly contained two centrifugal pumps, one for the alcohol, and one for the oxygen, both connected to a common shaft. Hydrogen peroxide converted to steam, using a sodium permanganate catalyst powered the pump, which delivered 55 kg (120 pounds) of alcohol and 68 kg (150 pounds) of liquid oxygen per second to a combustion chamber at 1.5 MPa (210 psi). Dr. Thiel's development of the 25 ton rocket motor relied on pump feeding, rather than on the earlier pressure feeding. The motor used centrifugal injection, while using both regenerative cooling and film cooling. Film cooling admitted alcohol into the combustion chamber and exhaust nozzle under slight pressure through four rings of small perforations. The mushroom-shaped injection head was removed from the combustion chamber to a mixing chamber, the combustion chamber was made more spherical while being shortened from 6 to 1 foot in length, and the connection to the nozzle was made cone shaped. The resultant 1.5 ton chamber operated at a combustion pressure of 1.52 MPa (220 psi). Thiel's 1.5 ton chamber was then scaled up to a 4.5 ton motor by arranging three injection heads above the combustion chamber. By 1939, eighteen injection heads in two concentric circles at the head of the 3 mm (0.12-inch) thick sheet-steel chamber, were used to make the 25 ton motor. The warhead was another source of trouble. The explosive used was amatol 60/40 detonated by an electric contact fuze. Amatol had the advantage of stability, and the warhead was protected by a thick layer of glass wool, but even so it could still explode during the re-entry phase. The warhead weighed and contained of explosive. The warhead's percentage by weight that was explosive was 93%, a very great percentage when compared with other types of munition. A protective layer of glass wool was also used for the fuel tanks so the