weapons manufacture is these day a long term thing, not easy as building Spitfires and Mosquito's was in the past.
My impression from reading is that it was actually quite long term even then e.g. the merlin engine was developed in 1933 according to wikipedia and I remember reading that it had a lot of problems. But fortunately it was there and in good shape when it was needed.
So an engine might be a thing you want to keep developing as a continuous effort because it is an enabler for various different possible aircraft.
I suggest that the software might be similar - not easy to do in a hurry.