There has been no official statement of what the mortars in the Brothers in Arms series are but are constantly
referred to simply as 'mortars' so a basic history of the Granatwerfer 34, which chances are the mortars used in BiA is presented here. The 8.1 cm mortar gained reputation in the history of WWII as one of the most accurate mortars ever developed and its steady stream of shells merely increased its capability in the field, it also uses a larger mortar shell then the American M2 mortar. (which uses 6 cm shell) The weapon was mostly issued to infantry teams of two who would set-up the mortars and carry it with them. Its body could be broken into three individual blocks, the barrel, baseplate, and bipod.
It's quite simple really to know if a mortar is around. If there are rocketing explosions everywhere, dirt in your face, and there isn't an enemy tank in sight it's most likely a mortar. The key to avoiding mortar shells is to continuously move about, never staying in the same spot and wish for luck. A close hit will stun you but a perfect-landing shell can automatically kill you and your men, its possible that your whole team be wiped out by a single mortar round. The only way to destroy a mortar is to quickly locate it and rush up and assault its crew. Grenades and Panzerfaust also effective against them, especially if the crews are still operating the mortar. Once you have homed in on them the crew will automatically abandon the mortar and scurry to take cover. If you need to assault the mortar position, strike it with all of your teammate is recommended. Especially in the mid-game, you should have 6 teammates. If there are other enemy team covering the mortar, you can use assault team to deal with nearby enemy squad, base of fire team against the mortar crew. The mortar cannot be used by you in the campaign. The mortars fire in a straight line of 4 shells per barrage. The Mortar is no longer seen in Hell's Highway, its seems that the FlaK 36 takes it place as light artillery.