Hints:

If you're having trouble aiming, follow the path
of your tracer fire or make your own crosshairs
with Scotch tape and stick it on the monitor.

Conserve heat-seeking missiles for either tanks or planes. Deal with helicopters with standard artillery fire.

The only reason you should use your handgun is to pick off supply crates that drop in.

Switch to the Antitank gun when the big chunks of metal start rolling in.

Try to pick off enemy foot soldiers while they're still in the boat. You should be able to wipe out all of them with a direct missile hit.

Change Level Settings:

Under the beachhead directory you'll see a list
of all the levels in the game:

Level_00
Level_01
Level_02 etc to Level_60

If you open those in notepad you can modify any of the levels settings. Incuding type of ammo and the enemys agression...

//Bullets,
Projectiles, Missiles
Ammo 250 15 15
Time 120
//Tank, Jet, HelicopterGun, HelicopterRocket (range:1-9)
Aggression 6 6 6 6

Just change the numbers beside "Ammo" to whatever
you want, or lower the agression of the enemies
to give yourself a little breathing space.