The Schlüsselgerät 41, or SG-41, a complex cryptographic machine used by the Nazis during World War II, is now available online. The German military developed a replacement for the Enigma, but only 1,000 were ever produced due to material shortages and heavy weight. Despite its complexity, it was never able to fully replace the legendary Enigma. The British cryptographic wizards at Bletchley Park were initially bewildered by its messages and the US Signal Security Agency called it a "remarkable machine". The SG-419 was first produced in 1941 and used four levels of encryption, with a key sequence of six letters issued daily and a table of pin configurations reissued every month.