Project HARP, short for High Altitude Research Project, was a joint project of The Pentagon and the Canadian Defense Department created with the goal of studying ballistics of re-entry vehicles at low cost; whereas most such projects used expensive (and failure-prone) rockets, HARP used a very large gun to fire the models to high altitudes and speeds. Started in 1961, it was created largely due to lobbying from Gerald Bull, a controversial but highly successful ballistics engineer who went on to head the project. His ultimate goal was to fire a payload into space from a gun, and many have suggested that the ballistics study was offered up simply to gain funding. The project received just over 10 million dollars during its lifetime.
The project was based on a flight range in Barbados, from which shells were fired eastward toward the Atlantic. Using a 20 meter, 40cm caliber navy gun (later extended to 40 meters), the team was able to fire a 180kg slug at 3600 m/s, reaching an altitude of 180 kilometers. While the speed wasn't nearly enough to reach orbit, it was a major achievement given a budget dwarfed by most ballistic missile programs.
The program was cancelled shortly after this. Most of the criticism was focused upon Bull and whether a ballisticly fired payload could ever reach orbit, although the politics of the Vietnam war and soured Canadian/US relations played their role as well.
While it is questionable whether projectiles could ever be directly fired as a single stage from Earth without the use of exotic materials in construction, HARP demostrated an efficient way to launch a projectile part of the way. Additionally, it showed that electronics could survive such a launch, making it possible that a sabot-fired rocket could launch once it reaches its peak altitude, and continue the rest of the way into orbit.
A second incarnation of the HARP project, also conducted by Gerald Bull, was done in Iraq under the patronage of Saddam Hussein. The assassination of Bull and the 1991 Gulf War ended the project partway through development.
