How Pilots Started Aircraft With a Shotgun Shell

Starting a WWII aircraft engine required more engineering than most people realize. Electric starters needed heavy batteries and external charging equipment. Inertia starters cranked by hand took 10 to 20 seconds and had to be repeated from scratch if the engine didn’t catch. For aircraft with large radial engines operating from forward airstrips with no ground support equipment, neither option was ideal. The solution was a shotgun shell.

How It Worked

The Coffman engine starter, commonly called the shotgun starter, used a standard cordite cartridge inserted into a breech connected to the engine by a short steel pipe. The pilot fired the cartridge electrically or mechanically from the cockpit. High-pressure gas shot down the pipe, drove a piston through a screw thread, engaged the starter ring gear on the crankshaft, and turned the engine over. The entire sequence happened in seconds with no external equipment required.

The system was lightweight, compact, and self-contained. Unlike electric starters it added no battery weight to the aircraft and required no ground power unit. The carts sometimes mistaken for fuel trolleys on period photographs are often battery starter trolleys providing external power for electric starters, which gives some indication of how cumbersome the electric alternative actually was in field conditions.

Where It Was Used

Coffman starters were most common on American aircraft with large radial engines, particularly those powered by Pratt and Whitney Wasp variants. The F4U Corsair is among the most well-known examples. British aircraft also used cartridge starters including the Supermarine Spitfire and Hawker Typhoon on certain variants. The system extended beyond aircraft into tanks and tractors. The Field Marshall diesel tractor used a shotgun cartridge fired by a hammer to drive the engine piston directly through its stroke, a simpler application of the same principle.

Cartridge starters even appeared on early jet engines. The English Electric Canberra used a high-volume gas cartridge driving a turbine rather than a piston to initiate the engine start sequence.

The Tradeoff

The one genuine disadvantage was consumability. Every start attempt used one cartridge. A flooded engine or a false start meant reaching for another round. This was mitigated by the fact that air compressor starting systems used the same mechanical principles and could be fitted to aircraft already equipped with shotgun starters, giving ground crews an alternative when cartridge supply was a concern.

Hand propping, the practice of spinning the propeller to start an engine by hand, was not used on large WWII radial engines. What appears to be hand propping in period footage is typically a procedure to clear oil that has pooled in the lower cylinders of a radial engine after shutdown, preventing hydraulic lock when the engine is started. The actual starting was handled by the cartridge in the breech.

Electric starter technology improved significantly after WWII and the shotgun starter declined rapidly. The aircraft that carried them are now museum pieces, and the cartridge breech fitted behind the engine cowling is one of the details most visitors walk past without recognizing what it was for.