Halfway through the Aircraft Carrier mission, when you open the hanger doors to get to the missile area to sink the carrier, there will be a checkpoint.
Immediately after this checkpoint, the big hanger doors will open, and a Heavy Armour guy will be standing there.
Take a rocket launcher onto this level, and you can 1 hit kill him each time. Kill him, reload checkpoint, kill him, reload checkpoint, etc.
Takes longer to reload the checkpoint than it does to kill him :P