When I have two units that start with the "M252_US_Bag_EP1" and "Tripod_Bag" respectively, they can assemble the mortar just fine, however they can't enter it! It seems locked from entry?
Placing the M252 on the map, you also need to have it unlocked to be able to man and fire it. So I think it is locked by default.
Is there a way to unlock it and still have the units start the mission with the mortar dissassembled and on their backs? MP by the way.