The 'Harvey Wall Banger' was developed as an effective alternative to high explosives as a means of gaining entry through walls - experience having shown explosives to possibly be an unsatisfactory option, particularly in hostage situations.

Using the H.W.B. method it is possible to establish entry rapidly, enabling a team to gain access at the moment of breaching while minimising structural damage and risk to the hostages. The H.W.B. achieves this by launching a water filled plastic container at a velocity sufficient to breach the wall, with the accumulated kinetic energy being instantly and safely dissipated upon impact.

Propulsion is by compressed air, with the rear of the H.W.B's smooth-bore barrel being divided into an air reservoir separated from the main barrel by an entrapped glass disc. This disc ruptures by electrical detonation at a given pressure, thus applying instantaneous pressure to the rear of the projectile. A loose piston prevents any leakage of air past the projectile, giving good velocity at pressures between 200, 400 and 600 psi.
The complete system comprises 2 cannons, 10 glass burst discs fitted with No.8 electric detonators and 10 containers in a storage crate (6 reinforced, 4 plain). Each cannon is stored in a strong wooden box with piston, 5 burst discs, H.P. air cylinder and control box.
The system has proved easily transportable in both a scout helicopter and an estate car. It can be carried comfortably by a four-man team and is compact enough to pass through any standard doorway.