Well these are not real small but they are small,-
F107-WR-101 turbofan-which powerd a USAF AGM-86B Air Launched Cruise Missile-
F-121 fanjet-which powerd a AGM-136A Tacit Rainbow-
And no Sushka the APU is not the smallest jet engine,They make mini turbos that are the size of a film case now that is small-cheers!!!!!!