So you need to Pick a problem: dig in under fire

It's 1914. Machine guns and artillery make standing in an open field suicide.

1. So you dig a ditch and get in it.
2. But one enemy at the far end can fire down a straight ditch's entire length.
3. So you dig it in a zigzag, with blocks of earth called traverses.
4. But two meters deep, you can't see out.
5. So you cut a fire step to stand on.
6. But then it rains, and the walls slide in.
7. So you shore them up with sandbags, timber and corrugated iron, and lay duckboards over a drain.

The enemy does exactly the same. For over three years, the Western Front barely moved.