Item description:

Demolish Part 2
Campaign: demolish 50 houses

"Heavy Metal" Mission

Should be 20/21 buildings left to demolish

You're in the UAV, there are just over 12 buildings,
and most will go down with 1 hit from the UAV's missile

Be sure to shoot the guys on the rooftops first,
so they don't shoot your UAV down

Once you've have demolished around 12 buildings,
pause the game and reload checkpoint (it'll keep your stats),
then demolish the remainder

NOTE: Resign and rehash as always