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 project was established to create a cartoonishly large gun to shoot things into space. The sole fruit of this partnership, a massive toppled gun barrel, still remains on the Barbados test site.
Now, that's a gun... a 100 caliber monster based off of a U.S. Navy 16 inch gun. Yes, they started the project with a battleship gun capable of launching two and a half tons 23 miles, and then scaled it up. Way up.
Wikipedia, of course, has a good bit of information as well:
Started in 1961, HARP was created largely due to lobbying from Gerald Bull, a controversial but highly successful ballistics engineer who went on to head the project...
Bull's ultimate goal was to fire a payload into space from a gun, and many have suggested that the ballistics study was offered simply to gain funding. While the speed was not nearly enough to reach orbit (less than half of the 9,000 m/s delta-v required to reach Low Earth Orbit), it was a major achievement at much lower cost than most ballistic missile programs.
For more detail - a lot more detail - you can read "A Brief History of the HARP Project" at Encyclopedia Aeronautica. It's a fascinating story of strong personalities, politics, and engineering.
The March 1990 assassination of Bull (allegedly at the hands of the Israeli Mossad or the Iranian VEVAK intelligence agency) in his Brussels apartment, and the 1991 Gulf War ended the project.