Blow up Hitler on VIP boat with a sea mine.
Probably the easiest way to kill Hitler. Tag the mine that's right in front of you as you start, then tag Hitler, then enter the base and fire a few shots to make him panick and flee. Wait until he's just about to enter the VIP boat and shoot the attachment where the mine is, as it hangs above the boat. It will cause the mine to drop and explode.