I found it interesting to compare the performance of state of the art electric-powered railguns (the US navy’s INP gun described in the article and
this promotional PDF document) to powder-powered “superguns” (The US and Canadian defense departments’ 1960s
HARP project guns, and Iraq’s never completed 1980s
Project Babylon gun). The INP gun’s nearly-achieved design goal is a roughly 2500 m/s muzzle speed, while the best HARP gun achieved 3600 m/s. The stated goal of the Project Babylon gun was satellite launching, so we can assume it was intended to achieve a muzzle velocity on the order of 10000 m/s, though its unlikely anyone will ever know for sure, as the unassembled gun is believed to have been dismantled and destroyed after the 1991 Gulf War, and both supergun projects’ chief designer and proponent,
Gerald Bull, was killed at his home in 1990.
Beyond performance, similarities between the old big powder superguns and the new railguns end. Bull’s guns were huge – the largest HARP gun 40 m long, the Babylon gun to be 156 m long, while INP guns, intended to be fit in ship gun turrets, appear to be about 10 m long. Superguns are pretty much self-contained, while INP guns are cabled to an array of capacitors (or special mechanical alternators) larger and more massive than the gun itself. Superguns require gunpowder or other explosives, while railguns require electricity. The production version of the 32 MJ prototype INP gun is planned to require 64 MJ, not a lot of energy by naval standards – a
Nimitz class supercarrier generates a total of about 200 MW = 200 MJ/second, while a
Seawolf class sub generates about 30 MW. A modern heavy tank typically has about 1 MW, so tank or other mobile land-based railguns, presumably smaller versions, seem practical.
Comparing the INP railgun to older gunpowder superguns, and various vehicles
