In the campaign Steel Pegasus, during the first mission LZ Nowhere you have an optional objective to retreive a friendly mortar.
Upon dissasembling that mortar, you're only given the tube and no tripod.
Once you retreive that tube, the objective is completed but as you bring it to the ERP, there is a tripod on the ground which i assume was meant to be for the mortar.
Only problem here being is that the tripod is for the AAF faction and therefore incompatible with the NATO mortar tube.
Due to that reason you cannot use the mortar against the incoming enemy attack.