It has been stated Jules Verne chose a super gun for his story because he felt that no one would believe that a rocket could actually transport people to the moon.
For many years, it was believed that the only practical way to launch anything into space was to use gun propulsion because, at that time, rockets were still pretty small and were powered by gunpowder. In the 1930s, the first liquid propellant rockets were developed. Gun propulsion was soon abandoned as a means of space launching.
However, in the 1960s, gun propulsion was back in play. HARP (High Altitude Research Project) was a joint initiative between the American and Canadian defense departments. Its original purpose was to analyze the ionosphere and investigate the potential for developing ionospheric enhanced technology for radio communications and surveillance.
The project began in 1961. The island of Barbados was chosen as its launch site (apparently because Barbadians couldn’t complain about the noise of the big gun).
Canadian ballistic engineer Gerald Bull designed the HARP gun. The first model was constructed from a 50-caliber naval cannon like those found on battleships. However, this model proved ineffective, so the next cannon’s size was doubled to 100 caliber. This made it much too big for use by the military, but had the potential to deliver satellites into orbit. Consequently, its purpose was modified to determine if the super gun was capable of delivering objects into the upper atmosphere and eventually into orbit.
In January 1963, the big gun roared into life for the first time, sending a test payload into the sky. This was the first time in history that a gun of this size had been fired at a near vertical angle. With a launch velocity of 3300 feet per second, the wooden slug rose to an altitude of just under two miles before coming down a about a half mile off shore.
Subsequent improvements allowed the gun to fire an object almost 600,000 feet (112 miles) into the sky, setting a world record for gun-launched altitude. Even so, this is far short for a low-orbit satellite (around 1200 miles).
In 1967, funding ceased for HARP. Over the next decades, the giant space gun was left to rust at its original launch site on Barbados.
In 1981, the Iraqi government contacted Bull for the purpose of designing artillery during the Iraq-Iran war. At this time, Saddam Hussein was the Iraqi defense secretary.
Seven years later, Bull was provided $25 million by the Iraqi government to begin Project Baby Babylon. The huge gun had the potential to become a true space gun as well as a terrifying military weapon.
While the space feature was never fully developed, its use as a military weapon was. Its Achilles heal was that due to its immense size, it could not have been moved once it was put in place. This would make it easy to locate and then take out with an aerial attack.
In 1990, Bull was shot five times as he entered his Brussels apartment. His key was still in the door and $20,000 in his briefcase were untouched. There were no witnesses. Although the killer was never found, suspicion fell to the Israeli Mossad.
With his death, Baby Babylon was abandoned by the Iraqis.