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 a joint initiative between the United States and Canada to research the use of ballistics to deliver objects into the upper atmosphere and beyond.
In lay terms, the HARP project was established to create a cartoonishly large gun to shoot things into space. Designed by mad ballistics engineer Gerald Bull, 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 able to fire an object a staggering 112 miles into the sky, setting the 1963 world record for gun-launched altitude at 93 KM.
As the project continued, similar guns were built in locations across the United States, however, the sole surviving fruit of the project is the massive, toppled gun barrel at the Barbados test site. The Barbados gun was abandoned in the late 1960s and left to rust on its original launch site and after years of neglect looks more like a painted sewer pipe than a Godzilla-size gun barrel. Please note that the gun is located on an active military base and is only accessible with permission. If you really want to do it the right way, contact the military base a couple of months before you go and get their written permission.
UPDATE August 2014 : The cannon is now almost totally disappearing under the bushes, and the rust is eating it fast.
UPDATE May 2017: The longer cannon is still easily visible, the secondary one is now hidden in the undergrowth about 10m to the NE of the larger one, sections of its barrel are just visible.