Paratrooper is based on the similarly named arcade game from the past as well as the classic Airborne! Macintosh game.
In this game you control a turret and mortar. Use the turret to destroy enemies in the sky. Use the mortar to destroy enemies on the ground. Occasionally a fighter jet will appear and attack your base with a rocket. Also paratroopers will attack you when they reach sufficient numbers.
The goal is to try to stay alive as long as possible.