V-3

The V-3, also known as the Hochdruckpumpe ("High Pressure Pump", HDP for short; this was a code name used to hide the real purpose of the project), was a German World War II supergun working on the multi-charge principle whereby secondary charges are detonated to add velocity to a projectile.

The weapon was planned to be used to bombard London from two large bunkers in the Pas-de-Calais region of northern France, which were rendered unusable by Allied bombing raids before completion. Two similar guns were used to bombard the country of Luxembourg from December 1944 to February 1945.

The gun used multiple propelling charges placed along the barrel's length and timed to fire as soon as the projectile passed them by, to provide an additional boost. Due to their higher suitability and ease of use, solid-fuel rocket boosters were used instead of explosive charges. These were arranged in symmetrical pairs along the length of the barrel, angled to project their thrust against the base of the projectile after it passed. This layout spawned the German codename Tausendfüßler ("millipede"). Unlike conventional rifled weapons of the day, the smooth-bore gun fired a fin-stabilized shell, dependent upon aerodynamic rather than gyroscopic forces to prevent tumbling, which resulted in a higher drag coefficient.