Former submariner:

The military is about as far from zero-sum as you can get.

Gear is manufactured, used, worn out and discarded, at surprisingly high cost overall.

Soldiers are recruited, trained, serve, and leave. Training funds, time, and gear are necessary but never recouped.

Every military operation of any scale uses food/fuel/every other supply imaginable - all used and lost from other productive use.

Every 'build a civilization' game ever assigns expenses to military units created, never any production value.

(Ok, military R&D is sometimes practical and useful outside of the military... a small sop in an other wise large sinkhole.)