While not terribly advanced tactically or technologically, your enemy is nothing if not tenacious. Since your gun is located in an inaccesible location, enemy forces are dropped over your position by parachute, giving you the opportunity to kill them in the air before they can land and organize an unstoppable assault against your ground defenses. There are four types of enemy paratroopers:
Your basic, standard-issue paratrooper, dressed in standard-issue green jungle camouflage. Grunts are numerous, but they carry only light weapons so they are not too dangerous -- in small numbers.
 
Special Forces Trooper
These elite troops are decked-out in low-visibility night camouflage gear. They use steerable parafoils instead of common parachutes, and their special equipment and training make them effective and dangerous once on the ground.
 
Airborne Engineer
The enemy engineers are still wearing their brown desert camouflage from the last war. Each one carries a demolition charge which they will drop on your gun and ground defenses to soften them up before the assault. While their demolition charges are deadly, the engineers themselves are lightly equipped and relatively harmless once they reach the ground.
 
Commander
Due to quaint notions about honor and courage under fire, the enemy commanders wear bright red ceremonial uniforms so everyone knows who they are. By killing them in the air, you can demoralize the enemy troops. If they land, however, they will quickly organize their forces into an effective unit, so kill them quickly.
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If your defensive efforts succeed in repelling your enemy's attacks, they may become frustrated and resort to other tactics. Keep your head down!
Once the news of the enemy attack reaches your headquarters, additional supplies will be sent to reinforce your position. Because of your remote location, the quickest way to get vital supplies to you is by airdrop. Specially-selected "volunteers" in blue jumpsuits, loaded down with ammunition, spare parts, and letters from home, will appear from time to time. They're on your side; don't shoot them. If they can land and reach your gun emplacement without being killed by enemy ground troops or over-zealous defensive fire on your part, they will deliver their supplies, which will be available before the next raid arrives.