The army is the final boss fight in the game (in the desert patrol story line). There are a total of 8 regiments but you only have to defeat arround 3 (exact number seems to depend on which regiments you attack) and the Desert Patrol will take care of the rest.
You will need 15-20 men all equiped with RPG 7's, M67's, and military armour (if RPG's are too heavy go for M14's but at least half of your guys should have them). I wouldn't advise having more than 20 because they will get in each others way making them easy targets for enemy rocketiers/grenadiers.
High AP is very important, apart from the obvious advantage of being able to do more, high AP units go first in battle. And you do not want the army to go first.
(From Whirled): Close enough, except that you've gotta keep in mind that M14's won't work at all. The only useful guns for this are RPG 7s, snipers, and machineguns. RPG 7s are preferred, but keep snipers for those few "stand-alone" guys who stay away from groups.
Use RPG's/M14's early then switch to grenade once they enter throwing distance. When the battle first starts you should focus on killing the soldiers equiped with rocket launchers first. Then move on to kill the grenadiers (if they are in throwing distance before you have killed all the rocketiers target them first). With explosives out of the way you should just start targeting the biggest groups possible, only the machine gunners are any real danger now.
After you defeat the first unit go to Qubba and heal your soldiers, repair your vehicles (the army is about the only thing in the game that can actually damage them much) and replace ammo used.
Save the game (make sure you have a seperate save from before you start the attack) and wait for Desert Patrol to arrive to give you an idea as to how many more regiments you need to defeat. Load the save and repeat the process until between you and Desert Patrol you have defeated all of the regiments with at least some of the Desert Patrol remaining.
(From Whirled): Cheapos. You should fight as many of them as you can. That is, if you want to die.