Those were used to destroy the mines they placed.
They were also used to clear razor wire, I'm pretty sure.
As for the build, the idea and mechanics have the potential to be extremly fun. Though I think you should work on filling the beach with more craters and such, and add atleast a little bit more of detail to the wall and bunkers. On the other hand though I like how you extend the build to give a larger view of the beach but still restrict player movment.
Overall, looks like an awsome idea - just needs work.