Enter The Jerries

 
WWII GI has several enemies which all have different attributes.
Wermacht soldier
These are the most common enemy, they are armed with a Schmeisser and wait for you in parts of the playing field, when they see you they will shoot at you or even go after you. In missions where you are on the defensive these will walk towards friendly positions, sometimes shooting, until you or a friendly kills them.
Wermacht officer
These are armed only with a pistol and are harmless unless you are too close to one for too long. You get a morale boost for killing one and sometimes they tend to make their men go after you more readily.
SS Grenadiers
These are a little smarter and tougher than the Wermacht soldier. When there are more than one they tend to go after you in groups. Sometimes it seems as though I can't hit one even if I'm aiming right at him.
SS Officer
These are also armed with a pistol and you get more morale for killing one. They are also tougher than the Wermacht officer.
Sniper
These hide somewhere like in a window or bombed out building or sometimes in a hedgerow and wait for you. One shot can kill you and you should look out for these and use sniper rifle or BAR to kill them. There are a bunch in Saving Private McCurkee.
Machine gunner
These are usually in positions like bunkers or other protected structure and wait for you or other soldiers to move on their positions. These shoot rapidly and can put a quick hurting on you. They are more accurate than regular soldiers but do not move. Their assistant can't shoot at you.
Tanks
In this game the tanks do not move but they can turn their turret and shoot at you. Their shells explode and even a hit close to you may kill you. You can only kill a tank by shooting it with a bazooka or running up to it and laying a TNT or satchel charge on it.
Artillery Guns
Several missions have artillery guns. These are harmless but one mission requires you to find and attack the guns. The guns are usually hidden in a bunker or camouflaged earth emplacement, they are manned by at least 2 soldiers and usually are manned by 3 soldiers and an officer. There are also artillery vehicles like the SP gun and "panzerwerfer" rocket launcher. These are also harmless but you can not destroy them. They are also accompanied by some infantry.
Artillery barrages and air attacks
Enemy and Friendly air attacks are preprogrammed in some levels. In D-Day enemy artillery randomly falls until you get to the wall, then US aircraft bomb the installation and if you're not careful, you. In 88's a barrage starts when you start walking out of the forest. Urban rush has extensive barrages and you must be careful or pay the price. Sometimes enemy aircraft are triggered to make a strafing pass at you, you can sometimes see them but you can't shoot one down. If you hear a diving engine sound, duck for a wall, foxhole, building, or anything.