> In WW2 the Germans fitted aircraft engines to their tanks, which worked great when the engines ran, but too often they didn't due to battlefield conditions. (Germany was also terribly short of avgas, which crippled those tanks.)

This sounded interesting so I skimmed the tanks mentioned in [0] and only found mention of prototypes exploring use of a turboshaft engine [1] from [2]. [1] explicitly states "none of these was fitted operationally", so I don't get the impression that these ever even encountered battlefield conditions before Panther II was canceled.

[0] https://en.wikipedia.org/wiki/German_tanks_in_World_War_II

[1] https://en.wikipedia.org/wiki/GT_101

[2] https://en.wikipedia.org/wiki/Panther_II_tank#Engine

> Piston aircraft engines indeed need tons of maintenance.

Modern small piston aircraft engines under 250 HP have average TBO of 2,000 hours and can be operated beyond that with oil analysis. That's fine for commercial use, and piston engines only use 1/3 to 1/2 the fuel of jet engines, though that may be because of the use of a propeller.

So you trade fuel efficiency for engine maintenance, and I think they'd average out. DC-3 operators can maintain their piston engines just fine with one mechanic.

(Large turbofan engines like the 737 MAX uses are basically resurrecting the propeller in terms of moving a large volume of air, rather that relying on only a jet of air.)

I don't think there is a lot of data for larger piston engines. 1,000 HP engines and larger in WW2 had issues at the time, but that was 75 years ago. Metallurgy and production methods have improved since then.

Also WW2 engines were boosted (supercharged and water/alcohol-injected) and the military didn't care about longevity as airliners do today. For example, the American supercharged P-38 was the fastest fighter of WW2, while the version sold to Britain wasn't, and was a dog.

Source: commercially-rated pilot, WW2 student.