penetration of the shells due to limited maximum velocity, safety concerns with the breech blocks blowing out of guns, and higher skill levels demanded of gunners led the British Government to revert to rifled muzzle-loaders from 1865 to 1880, when Britain finally deployed reliable screw breech mechanisms. The Imperial Japanese Army used Armstrong cannon during the Boshin War to devastate the Aizu castle town and force its inhabitants to surrender quickly, and British Armstrong light field guns proved deadly against Chinese forces in the Second Opium War. However, the British Army and Navy preferred to revert to muzzle-loaders until larger high-powered breech-loaders with secure obturation systems that were relatively simple to operate were developed. Broadwell ring American engineer Lewis Wells Broadwell who worked as sales agent for the Gatling Gun Company in Europe replaced a papier-mache obturating cup in bag-loaded RBLs with a metallic gas ring and patented his invention in 1861, later perfecting it in 1864 and 1866; most countries paid royalties to Broadwell for the design, but in Germany the Krupp company stole it and used it for free. French efforts In the meantime the French persevered with trying to develop breechloaders which combined faster loading than muzzle-loaders, high power, safety and solved the problem of obturation. The Lahitolle 95 mm cannon of 1875 with an interrupted screw breech met the first three requirements to a great extent and partially solved the obturation problem. Finally the de Bange system introduced in 1877 solved the obturation problem with an asbestos pad impregnated with grease which expanded and sealed the breech on firing. The de Bange system formed the obturation system for all subsequent screw breeches to the present day. Britain adopted the de Bange breech when it returned to breechloaders in the early 1880s after some initial experiments with the inferior "Armstrong cup" obturation system. Britain, France and the United States preferred screw breeches for most calibres, but the major drawback of the de Bange interrupted screw as first implemented was that only half of the circumference of the breech block could be threaded, and hence it needed to be fairly long to achieve safe locking of the breech, which required three separate motions to open after firing; rotate to unscrew, retract the screw and swing to the side. Loading required the 3 operations in reverse. This was hence termed a "three motion block" and was slow to operate.