When you first play the mission you will be presented with a number of options.
The first being...

Attack or Defend
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Attack = Play as the the Americans, stroming the beach hell bent on gaining a foothold.

Defend = Play as the Germans, stand your ground and shout "THOU SHALL NOT PASS"... in german of course.

Difficulty
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Difficulty stacks unit numbers for factions. Easy gives players faction more than enemy. Hard the opposite and medium is even...ish.

Player Control
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This sets how many units the player gets to control at one time.
The Beach aims to put the player amidst the battle, assisting the ally AI. As oppossed to being in control of the entire faction.
Options available are "Light", "Medium" and "High" Player Control.

Starting Point
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Start at the begining of the mission, on the beach. Or start at the town behind the beach.