The few Germans on the board must hold out until help comes, but when the help does come, it is crack panzer and parachute units. The higher German morale usually means that they are hard to defeat and may often counterattack. You can paradrop the 82nd airborne division, behind enemy lines, or just drop them in your own zone to bring them on shore. You can try surprise attacks, and infiltration. Artillery can also bombard, but that is almost worthless.
Artillery can also support a defense.
Engineers can build fieldworks and fortifications, and can help in town assaults. Stacking is 5 battalions per hex, but only 2 batts. and a coy. can attack or defend. A breakthrough move and attack after combat is possible, but only if you start with a leader. There is a lot here, and when you first play this game, you will find yourself checking the rules frequently, and even movement will require a lot of chart checking. But none of this is complicated or unreasonable.