Not to be confused with the conspiracy factory known as Project HAARP (High-Frequency Active Aural Research Program), Project HARP (High Altitude Research Project) was responsible for building some of the largest cannons in history just to shoot stuff into orbit.
A joint initiative between the United States and Canada, Project HARP was established to research the use of ballistics to deliver objects into the upper atmosphere, or in lay terms, to create a cartoonishly large gun that could fire things into space. The project was headed up by mad ballistics engineer Gerald Bull, a military scientist who devoted his life to building super-size guns. Working out of a test site near an airport in Barbados, Bull and his team set about building their record-breaking cannon in 1962.
The gun itself was originally built from a 65-foot long, 16" naval cannon, the kind that might be seen on a battleship. The cannon was later joined to another barrel, extending the length of the gun to 130 feet and making it too big for effective military application, but (seemingly) perfect for satellite delivery. The titanic gun was not designed for delivering human subjects, but instead the cannon fired smaller projectiles in a sabot that would protect the payload during the firing and would fall away as the satellite rose. At its apex, the gun was firing payloads of tightly packed electronics thousands of meters into the sky.
Unfortunately the Barbados gun was never able to break orbit and after less than a decade of research, Project HARP was shut down in the mid-60's. Undeterred in his dream of sending payloads into orbit via colossal gun, Bull eventually went on to work with Saddam Hussein to build another cannon similar to the ones built with HARP. Sadly, Bull was assassinated with the use of a regular-sized gun in 1990.
Before it was discontinued, Project HARP built two other giant space guns, however the sole surviving fruit of the project is the massive, toppled barrel at the Barbados test site. The Barbados gun was abandoned in the late 1960's and left to rust on its original launch site. After years of neglect looks more like a painted sewer pipe than a Godzilla-size gun barrel.
[Edit: As many of our readers pointed out, our use of caliber and bore in the original article were not accurate in describing the weapon's size, and have been updated to reflect its true proportions.]