Getting to the barbed wire fences on your first couple tries makes a huge difference when you are on the attacking side of Operation Neptune. If you use this route, I guarantee you will be more succesful. After numerous war games this route is the most consistent.

1. First you make your to the right towards the tank
2. Go left to hedgehog wall
3. Go rigth and you'll reach the seawall and the barbedwire fences

Move in L shaped patterns like a knight in chess. Always try to have a piece of cover between you and the bunker on the right, that one is the most dangerous to you. There is a chance the benker on the left will get you but there is always a chance you get shot no matter what route you take.

Here is a video example of the run I'm stalking about. I've also included a very succesful run where I use this route, kill every enemy in one bunker and we finish the first stage almost instantly.

There are some other tips that will make you more succesful in this stage of the game.
1. Use smoke grenades. Partially blocking vision of the machine guns means the chances of you getting shot are smaller.
2. Use the Airborne division. It gives you faster movement speed which means you'll be out of cover for a shorter amount of time.
3. Grab the flamethrower. It is a powerful weapon, especially inside the B bunker.