The initial velocities of fragments from bombs, shell and grenades were studied in order to compare efficiencies of the various projectiles. Initial velocities may be predicted from a knowledge of the dimensions of the metal casing and the character and quantity of explosive. A theory was put forward that the contribution to the kinetic energy made by the detonation of unit mass of explosive is independent of the size of the projectiles. In a large bomb the explosion gases have actually more kinetic energy than the fragments. A simple expression is found for the average initial velocity in terms of the charge-weight ratio, C/M; this expression is found to agree with the experimental data fairly well over the whole range from C/M = 0.06 to C/M = 5.6.