The first wartime naval Enigma machine (M3) was identical to the model
used by the German Army and Air Force, but it was issued with additional
rotors, VI, VII and VIII, which were reserved for the Kriegsmarine (German
Navy). However, the Navy also employed codebooks to shorten signals as
a precaution against shore high-frequency direction-finding, and some manual
ciphers. The most important codebooks were the Kurzsignalheft (short signal
book) for reports such as sighting convoys, and the Wetterkurzschlüssel
(weather short signal book) for weather reports. 
Naval Enigma signals used different ciphers, each with its own daily key . The principal cipher was Heimisch (Heimische Gewässer - known to Bletchley Park as Dolphin) for U-boats and surface ships in 'Home Waters', including the Atlantic. At least 14 other naval Enigma ciphers were used later in the war.
The British codebreakers at Bletchley Park received an Enigma machine and rotors I to V from the Polish Cipher Bureau in August 1939. Marian Rejewski, an outstanding Polish cryptanalyst, had reconstructed the wiring of rotors I to III at the end of 1932 using mathematical techniques, and the wiring of rotors IV and V before the war began. The British recovered rotors VI and VII from the crew of U-33 on 12 February 1940, while rotor VIII was captured in August 1940.
In May and June 1940, using cleartext and cipher text captured from Schiff 26, Hut 8 at Bletchley Park had solved some April naval Enigma traffic with the aid of the first bombe (a high speed key-finding aid). That bombe, which was Alan Turing's brainchild, was much slower than the bombes with the 'diagonal board' invented by Gordon Welchman. The improved bombe, with the board, entered service in mid-August.
For the Breaking of the Enigma click here.
