It's fascinating how complex aircraft can be, even in the 1930's and 40's. Even today, compared to hopping in your car, turning a key and then driving off, a simple plane like a Cessna 182 still requires you to run through a check list, including things like putting your mixture to RICH, adjusting propeller pitch for HIGH RPM, pre-setting power lever 1/2 centimeter, adjusting carb heat and priming. Once started, you have to adjust mixture again for taxi, take off, cruise etc. There's just a lot to keep an eye on.
Now something like an old DC-3 with its Pratt & Whitney R-1830 Twin Wasp 14 cylinder radials had a start sequence something like this:
Assume the normal preflight walkaround for fuel and oil checks, caps, drains, locks and covers has been done.
Pilots, having been strapped in, are ready. This procedure usually involves both. Using electric start, unlike a car engine the starter isn't directly turning the engine as that would take too much battery power. Instead, a flywheel is spun up and then engaged which spins the engine over.
Starting with engine #2 (starboard), with the booster pump running, the stopwatch is set to zero. The right seat occupant waits for the pilot's command to operate the right engine start switch.
Pilot - switches on IGNITION MASTER, operates primer for right engine three or four times, one second each time. This primes the top four cylinders of the second bank.
Pilot - right hand over right engine ignition switch, and gets ready to start the stopwatch with left hand. Calls out 'Energise', starts clock. Puts left hand back to primer switch.
Right seat - operates flywheel energizer for fifteen seconds at which time pilot calls out 'MESH'
Pilot - maintains pressure on starter switch while right seat engages right engine MESH switch to engage flywheel. Right seat watches to see if engine turns over.
Sometimes, the engine is turned over by hand, pulling several prop blades through (usually 7) to make sure that the bottom cylinders haven't collected too much oil and avoid hydraulic damage. If the engine was hand turned, the right seat watches for three blades to swing by before calling out. If the engine is not previously turned over, nine blades must go by before he calls out either 3/9.
Pilot - hearing the 3/9 call, selects right engine ignition to BOTH (battery and magneto) then moves right hand to mixture control lever. If the engine catches, to keep it running the pilot will blip the primer switch as necessary while moving the mixture control lever to AUTO-RICH. It might take a few seconds, when the engine is running on its own the pilot then moves right hand to engine throttle and calls 'ON THE THROTTLE', which is the signal for the right seat to release the START and MESH switches.
Pilot - advance throttle slowly to about 1,000 rpm. being careful not to exceed 1200 rpm. cold engine limit. As the engine oil warms, the speed will increase so watching the tachometer is necessary.
Admire large clouds of smoke and repeat start procedure for the left engine.
note; in case of dead batteries there is a hand crank available for the engine whereby someone does the task of turning a geared drive to wind up the flywheel to engage the starter. It is laborious and sometimes takes several tries.
https://www.youtube.com/watch?v=23iCuMl00nA