Welin breech block While working as a weapons designer for Thorsten Nordenfelt in London, Axel Welin solved this problem in 1889–1890 with his stepped interrupted screw Welin breech block. This had threads in sets of steps of increasing diameter so that instead of only half of the screw being threaded, the fraction threaded was number of steps / (1 + number of steps): i.e. if the block of a large gun had four steps of threads, 80% of the screw was threaded, allowing a much shorter screw and hence breech block. This allowed the block to be unscrewed and swung out in two motions – the "two motion interrupted screw" breech. Bofors ogival screw Also in the early 1890s, Arent Silfversparre of Bofors invented an ogival screw breech, similar to the Armstrong model in the way it eliminated the need to withdraw the screw before swinging it to the side. Bofors continued to use this in medium artillery into the 20th century. The Elswick conical screw breech is very similar in concept. The sliding block The German company Krupp in contrast, adopted "Horizontal sliding block" breeches, rather than screw breeches, for all artillery calibres up to 16 inch naval guns. This was similar in some ways to the original "Armstrong screw"; the shot and powder cartridge were inserted through the open rear end of the breech into the gun bore, and a steel block was slid home into a horizontal slot cut through the breech to close the rear end of the breech. However, unlike Armstrong, Krupp loaded the powder propellant in a metal cartridge case much like a large rifle cartridge, which expanded against the chamber wall on firing and effectively sealed the breech. The sliding block, in both horizontal and vertical forms, and metal cartridge case continued to be the preferred German breech system until after World War II, and is still used by some modern artillery. Quickfiring guns The first quick-firing light gun was the 1-inch Nordenfelt gun, built in Britain from 1880. The gun was expressly designed to defend larger warships against the new small fast-moving torpedo boats in the late 1870s to the early 1880s and was an enlarged version of the successful rifle-calibre Nordenfelt hand-cranked "machine gun" designed by Helge Palmcrantz. The gun fired a solid steel bullet with hardened tip and brass jacket. It was superseded for anti-torpedo boat defence in the mid-1880s