A countermass weapon including a launching tube open or openable in both ends. The launching tube houses a launchable unit, a countermass, a pressure chamber, a propellant charge that upon firing and combustion of the charge in cooperation with the pressure chamber and the countermass accelerates the launchable unit forwards in the tube at the same time as the countermass accelerates backwards in the tube, and a firing and supporting unit connected to the outside of the launching tube. The countermass is designed such that a forward directed recoil is obtained and the launching tube is designed to be disengageable from the firing and supporting unit during the forward directed recoil.