[headquarters]

not the regular ones you bury to have a tank drive over them -but old school trench warfare mines -were a trench position is so well defended that it would be inadvisable to attack they dug tunnels under it that could be miles long and employ thousands of diggers-then they filled it with explosives and blew the whole position up .

this of course was tried countered by the defenders digging their own counter tunnels to blow up the enemy or to break into their tunnel and fight them man to man etc

Again a very cool setting for gameplay imho.