surface using a 100 HP steam engine with a maximum speed of 9 kn, then it shut down its engine to dive. She was purchased by the Hellenic Navy and was delivered to Salamis Naval Base in 1886. Following the acceptance tests, she was never used again by the Hellenic Navy and was scrapped in 1901. Nordenfelt then built the Nordenfelt II (Abdülhamid) in 1886 and Nordenfelt III (Abdülmecid) in 1887, a pair of 30 metre long submarines with twin torpedo tubes, for the Ottoman Navy. Abdülhamid became the first submarine in history to fire a torpedo while submerged under water. The Nordenfelts had several faults. "It took as long as twelve hours to generate enough steam for submerged operations and about thirty minutes to dive. Once underwater, sudden changes in speed or direction triggered—in the words of a U.S. Navy intelligence report—"dangerous and eccentric movements." ...However, good public relations overcame bad design: Nordenfeldt always demonstrated his boats before a stellar crowd of crowned heads, and Nordenfeldt's submarines were regarded as the world standard." 1886–1887: Carl Gassner of Mainz, German Empire receives a patent for a zinc–carbon battery, among the earliest examples of dry cell batteries. Originally patented in the German Empire, Gassner also received patents from Austria-Hungary, Belgium, the French Third Republic, the United Kingdom of Great Britain and Ireland (all in 1886) and the United States (in 1887). Consumer dry cells would first appear in the 1890s. In 1887, Wilhelm Hellesen of Kalundborg, Denmark patented his own zinc–carbon battery. Within the year, Hellesen and V. Ludvigsen founded a factory in Frederiksberg, producing their batteries. 1886: Charles Martin Hall of Thompson Township, Geauga County, Ohio, and Paul Héroult of Thury-Harcourt, Normandy independently discover the same inexpensive method for producing aluminium, which became the first metal to attain widespread use since the prehistoric discovery of iron. The basic invention involves passing an electric current through a bath of alumina dissolved in cryolite, which results in a puddle of aluminum forming in the bottom of the retort. It has come to be known as the Hall-Héroult process. Often overlooked is that Hall did not work alone. His research partner was Julia Brainerd Hall, an older sister. She had studied chemistry at Oberlin College, helped with the experiments, took laboratory notes and gave business advice to Charles. 1886–1890: Herbert Akroyd Stuart of Halifax Yorkshire, England receives his first patent on a prototype