This map is a 2vs4 battle on the beaches of the normandy (the region in France, not the space ship). 4 players attempt to invade the land from the sea, and the other 2 defend the coast. Both sides start with some extra buildings and units, but the 2 defenders with much more. The invaders need to find a way to breach the defenses.
This map is also known as z_normandy amongst RA3 online players. There are A LOT of versions of it, but this is the oldest, original version (no bridges, no extra cannons on the beach).
This map was not created by me, I just happen to have many RA3 maps on my hard disk.