The Strategic Long Range Cannon could be a follow-up to supergun work that Gerard Bull started for Iraq from 1988-1990. It could be a long barrel using high-performance propellant powder.
The SLRC could also be a scaled up railgun.
The Army’s M109A7 Paladin self-propelled howitzer and the M777 towed howitzer are 155-millimeter guns with a maximum range of 18.6 miles. The Long Range Land Attack Projectile (canceled) for the Zumwalt destroyers were going to have a range of about 85 miles. The 16-inch guns of the Iowa-class battleships had a range of only 23 miles.
In 1967, Canadian artillery engineer Gerald Bull built the High Altitude Research Project which had a range of 111 miles. The HARP gun was 118 feet long.
The Harp launch guns could reach 2000 meters per second. If you used gas to power the projectiles, you could go much faster. They really replace the first 1.5 stages of a conventional launch vehicle.
In 1988, the Iraqi government paid Bull $25 million to begin Project Babylon. Project Babylon began life as three superguns; two full-sized Big Babylon 1000mm calibre guns and a prototype 350mm calibre gun called Baby Babylon. The full-size Big Babylon barrel would have been 156m in length with a one metre bore.
Gerard was building the Baby Babylon gun for Iraqi leader Saddam Hussein. It had a bore diameter of 330-millimeters and was one hundred feet long. It would have had a range of 400 miles.
Big Babylon would have had a bore diameter of 914 millimeters and could launch a 1,322 pound projectile up to 528 miles.