Yes, absolutely. Who do you think is fixing all the tanks, ships and planes? You think we outsource that shit?
For every person who fights there are ten who fix their various equipment. Go look up AFSCs and Navy rates and at least half are directly maintenance related.
Every branch has fixed wing aircraft and helicopters, Army and Marines have ground vehicles that need repaired, and the Navy has ships and submarines jam packed with warfare and fire control electronics. It's crazy you think otherwise and it's obvious you have no actual knowledge.