Lutjens' Intentions

[wadinga]

Hello Tommy,

With your knowledge of Kriegsmarine radio techniques and Enigma practice, was there no sequential message number or similar to indicate to the receiving station if a whole message had gone missing? Many messages seem to have a fairly random number (repeat?) after the "Fleet" designation, but I have no idea what it signifies. Is it true that when maintaining radio silence, not even an acknowledgement of successful reception would be made?

It is indeed strange that Brigg's Catalina was shot by flak at around 10:30 on 26th am but Lutjens' report is of a "wheeled aircraft" is missing part as "seit" should say when surveillance started, and being a Kurtsignale has no Uhrzeitgruppe and is logged at 11:54.

Is Group West's message that this report was received on the 38m band at strength 4 significant? Then the "Fuel urgent" is received on the 24.9m strength 3 to 4. Switching frequencies and low power maybe suggests further problems, but the transmissions after Ark Royal's hit seem perfectly normal.

All the best

wadinga

[tommy303]

Many messages seem to have a fairly random number (repeat?) after the "Fleet" designation

Could you give me an example? In many messages there was a letter count included in the header.

was there no sequential message number or similar to indicate to the receiving station if a whole message had gone missing?

With a long message that was broken up into parts so as not to exceed the limit for message length with a single encryption key, each part normally had something like "2t1 1" and "2t1 2" to indicate a two part message parts one and two. This was then followed by the letter count in each part and the encryption key which itself was double encrypted using both enigma and a double letter conversion table from a settings sheet unique to each day. Normally, when decoded at HQ, a multipart message was combined to form a single unified message, and a transcript of the message would probably not show the parts one and two, etc.

As far as switching frequencies, the Germans monitored specific frequencies at different times in a day when waiting for a message, while sending units had tables showing what frequency and at what times they should transmit on. That way both HQ and ships at sea would know what times to be monitoring for incoming messages and what frequency should be used. The power may or may not be important, but I suspect not.

Another consideration is 1941 saw some very strong solar activity, starting in January 1941 when shortwave communications was slightly affected and continuing on throughout most of the year with an almost complete shutdown of shortwave communication world wide in July 1941 and more difficulties on into September and December (one might recall the messages to Admiral Kimmel and General Short in Hawaii from Marshall prior to the attack on Dec 7 were sent by Western Union telegraph rather than radio--solar disturbances were the reason; there was also the sudden radio blackout during the Dodgers/Pirates baseball game that so enraged fans on Sept 18 1941--once more solar activity was to blame). One has to wonder if solar storms played a part in the Bismarck chase.

[tommy303]

Is it true that when maintaining radio silence, not even an acknowledgement of successful reception would be made?

Generally, yes. An acknowledgement would be unnecessary unless the sender specifically requested one.

[wadinga]

Earlier I highlighted

forenoon of the 24th. Messages with Uhrzeitgruppe 05:52 and short signal 07:05 seem never to have been received by Group North. He says Uhrzeitgruppe 06:32 and 08:01 did not get received (presumably acknowledged) until 13:26 -13:40 hrs and were sent several times before this.

Presumably HHvS in PG picked up the first two and added them in to what Group West had recorded, but obviously Bismarck kept transmitting the latter two until reception logged. At least the old uhrzetgruppe would warn the message was afew hours old.

Message examples 24th 15:30 "Gruppe West an Flotte 97" then at 15:47 "an Flotte 98 At 15:44 "an Floote 95" Then later the suffix drops down to single figures.

Thanks for making your expert knowledge available to all.

All the best

wadinga

[tommy303]

A typical header would have a series of numbers and other information:

BDU 1201/5/88 31

Which means, to Head Quarters Uboats (BDU), at 1201 hours/5th day of the month/message number 88 31 letter groups in message.

Another example would be:

KR KR An alle KR KR 1725/12/107 9

KR meant a wartime priority message, so it would work out to

Wartime Priority message to all stations 1725 hours 12th day of the month/message number 107 9 letter groups in message.

[tommy303]

I should add, that in some messages, probably reflecting a change in proceedure, an actual letter count is used instead of a letter group count. It is also worth noting that Heer and Luftwaffe messages were formatted in five-letter groups while Kriegsmarine messages used four-letter groups. In general, the length of message segments using a single setting key was 250 letters. Longer messages were broken down into multiple parts as alluded to previously.

[tommy303]

[Message examples 24th 15:30 "Gruppe West an Flotte 97" then at 15:47 "an Flotte 98 At 15:44 "an Floote 95" Then later the suffix drops down to single figures.

I have been rethinking the above examples. It is probable, but not certain, that the 97, 98, and 95 are the consecutive log numbers for sent messages, although it is rather odd that the 15:44 message has 95 when it should have had a number of 99 or higher. I suppose it is possible it was logged earlier but not sent immediately and therefore got out of sequence or perhaps had to be repeated several times until successfully acknowledged. Dropping down to single digits with later messages probably indicated a new day or new log sheet when the log starts over at 1.

[wadinga]

Hi Tommy and all,

I'm sure you are correct that there is a sequential reference to the signals and that the Uhrzeitgruppe usually is in a parallel sequence except presumably when a higher priority signal jumps the queue and gets an earlier Uhrzeitgruppe through priority coding.

It surprises me that transmissions from Bismarck do not apparently have this fairly simple check on whether transmissions have been missed.

As you know who pointed out, but as usual he was wrong, whereas we had uhrzeitgruppe for Group West we don't when Group North was handling things. Except we do. Logged at 17:36 on the 24th we have Group North to Fleet 06 Uhrzeitgruppe 16:45 but 10 minutes later the intelligence group send B-Leitstelle an Flotte 100 (difference sequence) uhrzeitgruppe 16:37 and another ten minutes later we have Group West an Flotte 07 with uhrzeitgruppe 17:11. So even a transition period between Groups North and West still keeps the message sequence.

I recently found another reference confirming the existence of the Long Signal allowing British D/Fing. In the Secret Listeners by Sinclair McKay describing the work of the British Y stations which intercepted encoded transmissions and sent the character groups to Bletchley Park for decoding is a description. "It was the listeners at RAF Chicksands who picked up this crucial transmission" However also quoted is Peter Budd a veteran signal interceptor himself, who credits another station at Scarborough. "But then they lost her . No one knew where she was. Then the admiral in charge of the Bismarck broke radio silence for an hour to send messages back to Berlin and everywhere. Can you imagine those operators in Scarborough - fifty of them who normally get just seconds to hear any kind of message from a German vessel- hear someone transmitting plain language. All the direction finding stations around the Atlantic ..... attained perfect positions."

Well the memory may be a little muddled, for the Long Signal was definitely encoded and only a narrow spread of stations got bearings, but we here we have the confirmation again that the four segment signal took a very long time to transmit at a time when Bismarck thought she was under surveillance but was in fact, not. There has been a lot of misinformed tosh about teleprinter speed transmissions but this was old fashioned handraulic morse key work and the Y station interceptors listened to it via headphones and wrote down the character groups with a pencil on a pad. There was no point in fast keying since the message had already gone wrong, maybe twice. So the message was sent carefully and deliberately to minimise chance of mishearing.

Is it possible that mere embarrassment over the earlier error led to Lutjens maintaining what appears to be a fairly sulky silence about his intentions even when fixed by the RAF and FAA for most of the following day? Group West's frustration in not getting clear information seeps out of their messages for me.

All the best

wadinga

[tommy303]

In telegraphist training, an operator had to be able to receive 100--110 characters per minute accurately and send at 60 in order to qualify. Many were of course faster still and an average of about 100 to 110 characters per minute both sending and receiving seems to have been the norm using the usual type naval morse key (such as the Junker morse key). This would mean, that a 250 character message segment, such as one of Luetjens' long message segments, could be sent in 2.5 to 4.1 minutes. Since accuracy in sending and receiving was critical in coded messages where the telegraphist is not able to form words in his head and needs instead to accurately send and take down characters, I would be inclined to assume about 3 minutes per message segment, or roughly 12 minutes to send the four part message, which in DF terms, is quite a long time.

Is it possible that mere embarrassment over the earlier error led to Lutjens maintaining what appears to be a fairly sulky silence about his intentions even when fixed by the RAF and FAA for most of the following day? Group West's frustration in not getting clear information seeps out of their messages for me.

Possibly, although the more probable situation was when radio silence was ordered, both transmitter and receiver were shut off completely. This was the result of B-Dienst scanners being able to pick up emissions of enemy radio sets that were nearby, even if not actively transmitting. This was particularly true of older morse sets, and supposedly, but unconfirmed, which might be tracked at up to 100nm. As mentioned previously, even newer units, such as the super-heterodyne sets used by the Kriegsmarine, gave off receiver noise or emissions which could be detected if nearby. The ability of the Germans to pick up stray radio emissions was well known to the Allies, and often convoys were under strict radio silence to the point that all radio equipment was turned off completely. It is likely that the Germans practiced the same radio discipline, turning on receivers only at specific times a message might be sent from somewhere. Each day had specific schedules to tune in and listen and these changed on a daily basis.

[tommy303]

Concerning speed of transmission of naval messages:

One of the requirements for men recruited as telegraphists in the Brtitish monitoring service and tasked with intercepting enemy wireless messages was the ability to accurately receive 22 words per minute. Using the 'Paris' standard, this would be 110 characters per minute, so one might take this as a maximum standard of what one might expect a German telegraphist to send, and many would be slower since, as Wadinga points out, accuracy of transmission and reception was much more important with coded messages than messages sent in the clear. There were some men, such as the American Ted McElroy who could receive an incredible 77wpm, but they were rare and top, expert telegraphists generally adjusted sending speed down to accommodate the average.

[wadinga]

Hi Tommy,

I don't think the morse speeds you are considering are a problem to reconcile with accounts of an hour of tramsmissions. HHvS specifically said the whole message was repeated whilst he was listening.

The B-Dienst team in Bismarck will have had a lot of spare time on their hands if they had to maintain receiver silence as well as transmitter silence. Do you really think receiver shutdown is a factor? Is there a pattern in Group West transmission times to suggest this limited listening time was followed? Also since Bismarck was under direct aircraft surveillance, once again there is no need to maintain any kind of radio silence and no need to use cryptic misinforming short messages.

As for Lutjens possibly being exhausted, and not thinking straight, well it is every officer's duty to delegate so he can rest and be at optimum performance when his efforts are most needed. He had plenty of staff to point out the advantages of keeping Group West informed on ETA for harbour preparations and air and marine escort effectiveness. However Bismarck kept transmissions to an absolute minimum until the last night during which transmissions zipped back and forth, albeit after Ark Royal's attack had made further silence unnecessary.

Nasty infestation of Troll on the Danish site.

All the best

wadinga

[tommy303]

The question of whether or not Bismarck went to complete radio silence, ie. shutting down receivers as well as not transmitting is a good question. Unfortunately one survivor, one of Bismarck's radio operators, who could have shed some light on that has since died. I personally feel that it is possible, perhaps probable that routine was followed as it was a matter of what we can do, then so can the enemy. I seem to recall a paper on the radio war, that the British leaked false information that they were tracking German radio transmitters at sea by listening for radio emissions, do doubt to give the Germans false evidence to keep them from thinking Enigma was compromised. This would have had the effect of inconveniencing the Germans and disrupting their radio communications without having to do anything directly and at the same time direct suspicions away from Enigma.

As far as B-Dienst goes, their scanners did not give off much of a signature, so one might presume they were listening in for any detectable sign that a nearby vessel had its receivers on. I am afraid, though, that there are more questions than answers as to exactly what was going on in the radio communications department on the Bismarck. B-Dienst may have kept their receiver on to scan for enemy messages, which would be the smart thing to do even at the risk of being detectable. I freely admit that I do not know, just that it seems worth while to throw out some possibilities based on German capabilities and Allied response to them.

Why Luetjens did not transmit his intentions or ETA once Bismarck had been found again--again, I can only conjecture as stated in previous posts.

[RNfanDan]

Spurious emissions and RF products were greatly reduced by simply disconnecting the feedline to the overhead aerials. This was easily accomplished via a simple grounding switch or "standby" circuit, very common in radio rooms for decades. There is nothing to be gained in repeatedly shutting down radio sets over short periods (radar equipment notwithstanding) ---in fact, the better if it was allowed to "idle" in those days, as their stability depended very greatly on the set's cabinet temperature, tube/valve operating temperatures, and even the humidity of the air in the radio room.

The stability of equipment in those days was a far cry from the ultra-stable, digitally-synthesized circuits of today; one simply could not fire-up a "cold" set and begin transmitting or tuning in, without allowing time for the gear to reach a stable state based on the factors noted above. Small corrections could be made to synch-up TR and RCV circuits between local sets, but that is NO guarantee that the shoreside equipment would be tuned exactly to the same frequency.

For this reason, the sets would have been kept at least at a minimal operating state of "idle" for critical circuits, especially oscillator components (which determine frequency). I also doubt that maximum key speeds would have been used in transmitting characters of a message; this, because such high speeds would easily cause "gaps" at times, due atmospheric and ionospheric fluctuations (or "band conditions", as we operators call it) including lightning---let alone anything the enemy may be attempting to cause.

This is why signals were repeated, the earliest form of error correction that could be made. Very high keying speeds were less useful than easing-back a bit, which could allow a receiving station to grab an extra dit or dah when phase shifts or interference were present. Getting a radio signal through to its recipient could at times be a very difficult undertaking, even in the best of circumstances and using CW, the best of modes then available on HF bands.

My ha-penny's worth...

Dan

[tommy303]

Excellent post Dan. Indeed I remember the old vacuum tube sets and their extended warm up periods before they were stable enough to tune. I also agree that most messages using the usual morse key were transmitted slowly to minimize abiguities or errors in transmission and receiving, particularly, as stated previously, when dealing with encyphered messages.

[wadinga]

Hi Tommy and Dan and All,

It seems to me the example you are thinking of is the ruse employed by a captured RAF crewman who managed to persuade his captors that the Metox radar detector/receiver employed by u-boats emitted a signal that could be homed in on by patrolling aircraft. U-boats were consequently instructed to keep their very useful Metox switched off by this entirely spurious claim.

Surely these very low intensity emissions must have been almost impossible to detect, since all interception and D/Fing accounts concentrate on active transmission rather "leakage" of signal from transmitters on stand by or indeed receivers in passive mode.

The "Secret Listeners" book refers to accurate receiving tests, with the A grade requiring "69 groups of 5 letter cypher in 3 minutes making not more than 8 mistakes." These top level listeners of the British Radio Security Service received pay of £7 per week whereas junior grade codebreakers at Bletchley only got £4!

All the best

wadinga