Some versions of the Rolls-Royce Merlin engine used in the British Supermarine Spitfire used the Coffman system as a starter.
Shotgun starters are composed of a breech, into which the cartridge is inserted, which is connected to the motor by a short steel pipe, which acts like a gun barrel.
When the aircraft's ignition is turned on and the cartridge is fired, high-velocity, high-pressure gas (~1,000 psi (6.9 MPa) at ~600 ft/s (180 m/s)) shoots down the pipe, forcing the motor to spin and engage the starter ring gear on the engine, which is attached to the crankshaft.
Electric starters required large, heavy, and often troublesome batteries to be carried on board, or external charging equipment had to be located at every place where the vehicle was anticipated to operate.
The Coffman system was more lightweight and compact than inertial starters or internal batteries, and it did not require any special auxiliary equipment, an important feature when operating in remote areas.