You're an old fart when in the 1940's, you could witness an aircraft being started with a gunpowder starter:
Gunpowder starters work by exploding a small cordite charge inside a combustion chamber. This effectively pushes the piston in that cylinder down, which forces the other pistons to move as well. One of the other pistons is invariably pushed toward top dead center, at which point the air fuel mixture is ignited, and the engine starts to run under its own power.
These starters were commonly used through the 1940s in aircraft applications.