Hut 8 faced two major problems in trying to break naval Enigma:

1.  Eight rotors could be arranged in 336 different ways (8x7x6), instead of 60 for Army or Luftwaffe Enigma (5x4x3). A bombe run using all the German Navy's rotor combinations took five times longer than for Army or Luftwaffe Enigma and bombes were very scarce until large numbers of US Navy bombes became operational in late 1943;
2.  'Cribs' (probable plain text, used to 'program' the bombes) were non-existent until mid-1941.        
 

Hut 8 broke Dolphin cryptanalytically from August 1941 onwards. It was helped because the order in which the rotors were inserted in Enigma changed only every two days. If a crib was available, a bombe run on the second day could therefore find the day's settings in under 20 minutes, saving much precious bombe time.

Manual weather ciphers broken by Bletchley's weather section in Hut 10 provided many cribs. The Atlantic U-boats made numerous weather reports, encoded on the Wetterkurzschlüssel before encipherment. From February 1941 on, Hut 10 broke general weather signals, enciphered with the naval manual meteorological cipher, which incorporated the U-boats' weather reports. In early May 1941, Bletchley received a copy of the 1940 edition of the Wetterkurzschlüssel from München and U-110. This enabled Hut 8 to reconstruct the U-boats' weather signals, and so obtain a second source of cribs. In addition, identical signals on subjects such as mine-clearing were sometimes sent using naval Enigma and another manual cipher, the Werftschlüssel ('dockyard cipher'). When Hut 4 broke the signals using Werftschlüssel, Hut 8 had more cribs.

Hut 8 suffered a massive reverse on 1 February 1942 when a new Enigma machine (M4) came into service on Triton (codenamed Shark by Hut 8), a special cipher for the Atlantic and Mediterranean U-boats. The combination of M4, Shark and a second edition of the Wetterkurzschlüssel proved devastating. Bletchley Park became blind against Shark for over 10 months. Fortunately, M4's fourth rotor (beta) was not interchangeable with rotors I to VIII. Beta increased M4's power by a factor of 26, but rotors could still only be mixed in 336 (8x7x6) different ways - not 3,024 (9x8x7x6).  (Confusing I know!)

The Wetterkurzschlüssel and Kurzsignalheft were retrieved from U-559 by Lieutenant Anthony Fasson, Able Seaman Colin Grazier (both were posthumously awarded the George Cross - Britain's second highest award for gallantry) and 16 year-old Tommy Brown (who survived to receive the George Medal). Without their bravery, Shark would not have been broken before four-rotor bombes came into service, if at all. The Allies (Britain, Canada and the United States) would not then have established naval supremacy in the Atlantic until the second half of 1943 at the earliest, which would have probably delayed the D-Day Normandy landings until 1945. Few acts of courage by three individuals can ever have had so far-reaching consequences. Without Ultra, the U-boats would still have been defeated in the long run, but the cost in human life in the global conflict would have been even more terrible than it was.