Mortars are nowadays mounted on movable bases, allowing them to be moved from one place to another and, correspondingly, allowing them to be rapidly moved from the emplacement. A problem in such solutions is the ability of said base, i.e. vehicle, to defend itself against possible attacks, and the use thereof for destroying close-range targets on the ground. A moving base provided with a heavy shell mortar is normally unable to carry heavy defensive facilities in addition to the shell mortar, instead, it is at most provided with a heavy machine gun or corresponding lighter armature. In such a situation, the vehicle needs to be able to use the shell mortar for also firing horizontally or below it, for which normal mortar shells and shell mortars are not suited. A mortar shell inside a normal shell mortar having a smooth barrel is able to move when the shell mortar is oriented in the horizontal direction or below it in the barrel in such a manner that it either falls from the barrel or moves to such an extent that the mortar shell does not go off.
This problem is solved in the solution according to WO application FI 98/00064, wherein a separate control piece and a locking piece are attached to the tail of a conventional mortar shell with a mechanical locking. The locking piece fractures in connection with the firing. In this solution, separate parts have to be added in between the mortar shell and the control piece, which complicate the fastening of the control piece.