U-505 is based on the historic clash between the USA and Nazi Germany Navies. US Navy had the mandate to seek and capture the deadly “Enigma Machine Codebook” as well as to find and destroy the notorious U-Boat. German submarine U-505 is a Type IXC U-boat of the German Kriegsmarine built for service during World War II. She was captured on 4 June 1944 by United States Navy. Codebooks and other secret materials from U-505 assisted Allied code breaking operations. She is one of six U-boats that were captured by Allied forces during World War II, and one of four large German World War II U-boats that survive as museum ships. The submarine was towed to Bermuda in secret. The US Navy classified the operation as top secret and managed to prevent its discovery by the Germans. Prime Minister Winston Churchill wrote "The only thing that really frightened me during the war was the U-Boat peril." An Enigma machine is any of a family of related electro-mechanical rotor machines used for the encryption and decryption of secret messages and were used with remarkable success by Nazi Germany before and during World War II. Capture and decryption of German ciphers of this machine was so important that it is believed that it hastened the end of the war by two years. Prime Minister Winston Churchill told Britain's King George VI after World War II: "It was thanks to Enigma that we won the war." U-505 was donated to the Museum of Science and Industry in Chicago, Illinois. The U-505 is now a museum ship, kept indoors in a climate controlled environment to prevent corrosion.