The invention relates to a method for launching a projectile and a launcher comprising a barrel (1) accommodating a. a projectile (2); b. a rocket motor (13) at the rear end of the projectile (2) comprising a first compartment containing a first propellant; c. a countermass (3) at the rear end of the barrel (1); and d. a second compartment between the rocket motor (13) and the countermass (3) containing a second propellant, wherein said first and second compartments form a high pressure chamber (6) subsequent to firing of the projectile (2).