Mission: Blood and Rust
Difficulty: Easy
At the beginning of mission 3 you will come across two friendly Titans with Lt. Shaver and Lt. Freeborn inside. They are fighting multiple enemy Titans and your job is to keep them save.
The best way to do this, is playing on easy and attacking the enemy Titans as fast as possible. Even on easy Lt. Shaver and Lt. Freeborn can go down fairly fast if you don't defend them.
Once you reached the entrance at the end of the narrow battlefield you will unlock the Close Shave achievement, if both friendly Titans are still standing.