HARP (High Altitude Research Project) was a program to study the upper atmosphere using instrumented projectiles shot from a cannon, conducted in the 1960s by researchers at McGill University, Montreal. The projectiles were cylindrical finned missiles, 20 centimeters wide and 1.7 meters long, with masses of 80–215 kilograms called Martlets, from an old name for the martin bird which appears on McGill's shield. The cannon that propelled the Martlets was built by Canadian engineer Gerald Bull from two ex-United States Navy 16-inch- (41-centimeter-) caliber cannon connected end-to-end. Located on the island of Barbados, it fired almost vertically, out over the Atlantic. Inside the barrel of the cannon, a Martlet was surrounded by a machined wooden casing known as a sabot which traveled up the 16-meter--long barrel at launch and then split apart as the Martlet headed upward at about 1.5 kilometers oer second having undergone an acceleration of 25,000g. Each shot produced a huge explosion that could be heard all over Barbados and a plume of fire rising hundreds of meters into the air. The Martlets carried payloads of metal chaff, chemical smoke, or meteorological balloons and were fitted with telemetry antennas for tracking their flight.

By the end of 1965, HARP had fired more than a hundred missiles to heights of over 80 km. In 19 November 1966, the Army Ballistics Research Laboratory used a HARP gun to launch an 84-kilograms Martlet to an altitude of 179 kilometers – a world record for a fired projectile that still stands.