Reservehandverfahren (RHV) was the naval hand cipher used when the Enigma couldn't be used. Both use the same message format, both were broken by the allies. However I can't find any real info about RHV, so if anyone here knows where I can find details like the cages and bigram tables please point me to them!

If this has already been discussed to death please point me to the forum. Otherwise, since M4 attacks haven't worked, perhaps it is the cipher that is wrong?

Hi Seth, welcome to Enigma@home.

I don't remember any discussion so far about RHV, and I suppose it's quite possible that we're currently missing out by not even looking at it. The messages originate from Cryptocellar: http://cryptocellar.org

I don't know anything about RHV, but I *think* the cyphertexts are treated as Enigma simply because that's what they were historically claimed to be. Some earlier messages proved this to be the case, while the current one is still ongoing. Maybe someone with more knowledge here can provide a better insight?

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I think it was Jim Gillogly who pointed out that since the vast majority of naval cipher intercepts were Enigma that it was almost certain that the remaining messages were also Engima, and at least 2 out of 3 were. But you can't tell from looking at the formats (which was intentional) until you try, and you've tried, so maybe it's RHV.

Or maybe the message is just so garbled it needs to be chopped into tiny pieces to decode any of it. The fact the the first 8 letters aren't even repeated correctly does not bode well for clarity, plus the extra letters at the end and the "?" and any other hidden errors. Not an easy problem at all.

Has anyone tried working backwards -- getting all the u-boat logs, matching them to all the intercepts, and seeing what's left? Maybe find a plaintext? Or I suppose far too many u-boats were lost for that...

Thanks for the like to cryptocellar, maybe they have some documents on RHV.

Hi Seth

Third M4 message:
CLXP LWRU.........?..CDXP LWRU VA


CLXP LWRU : "Kenngruppe" - indicator group (coded message key)

? : Lost charakter (not very fatal for decoding)

CDXP LWRU : copy of the "Kenngruppe" - 1 garbled charakter (M4 Messages contains a copy of the Kenngruppe at the end)

VA: International characters (Morse-Code) for end of message ! ...- .- (VA)


I wrote my own ENIGMA I / M3 / M4 Hillclimbing software. Including Index of coincidence (IC) / bi and tri gramm tests.

The "Looks"-message (FCLC QRKN) has a very low IC: 0.0579 and is very hard to climb due to many shortcuts and heavy repetitions eg: "...faelltynnnnnnooovier..." Not very close to the German language. When I cut this "..ynnnnnnooo.." the software climbs very easy!

"Schröder"-message (YKRB MGVA) IC: 0,0611 is ok and climbs very easy. This message includes shortcuts too, but they fit very well to the bi and tri gramm tables.

I´m convinced, the remaining M4 message is M4. But with many shortcuts, and repetitions and garbled characters. Hard to climb.

Does anyone knows the correct meaning of this:

T.O.R.1152/19/221

T.O.R --> Time Of Reception ?
1152 --> Time ?
19 --> Day of month ?
221 --> 221 ?

This is very interessting, because the Naval rotors changed only every 2 days!
LOOKS and SCHRÖDER message are coded on the same reflector/Greek/rotors !!!
B B241
Plugs (Stecker) changed every day...

Breaking M4 on a single PCs needs decades ...
Breaking M4 with fixed B B241 needs weeks...

Breaking ENIGMA I needs days/weeks...

Best regards

PS: I guess the three messages are within the Naval Enigma M4 "Blackout" Feb 1942 - Nov.1942 .