The first thing you do is to run up a beach guarded by MGs firing at you. Try to stick close to Pierson, generally he moves when it is safe and will sometimes take a hit for you. If you get hit, just restart the checkpoint and try again. The trophy / achievement pops when detonating the pole charge at the seawall.
Here is a video guide with English commentary!
Here is a playlist of guides for this game!
https://www.youtube.com/playlist?list=PL-HeW6XkKdUKe25WzwEqI...