R
Recruit an ai and place it in the mortar
Place an ai in the gunnerseat, get in a helicopter and auto hover directly above the mortar at a low altitude
Command the ai to fire the mortar on a position very close to the mortar to try and get the elevation of the mortar as close as it can be to vertical
Once the helicopter is hit and has crashed take control of the ai in the gunnerseat and start firing