This is pretty interesting stuff: the M4 Message Breaking Project tries to break Enigma M4 messages intercepted in the North Atlantic during World War II. From the project website:
The M4 Project is an effort to break 3 original Enigma messages with the help of distributed computing. The signals were intercepted in the North Atlantic in 1942 and are believed to be unbroken. Ralph Erskine has presented the intercepts in a letter to the journal Cryptologia. The signals were presumably enciphered with the four rotor Enigma M4 - hence the name of the project.
They provide Free Software clients (GPL'd, written in Python and C) for Unix-like operating systems and various Windows variants. Project updates are available from the project blog.

The first message has already been successfully broken. The translated plain-text reads:
1930 Radio signal 1851/19/252:
" F T 1132/19 contents:
Forced to submerge during attack.
Depth charges. Last enemy position 0830h
AJ 9863, [course] 220 degrees, [speed] 8 knots. [I am] following [the enemy].
[barometer] falls 14 mb, [wind] nor-nor-east, [force] 4, visibility 10 [nautical miles].
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