G  E  H  E   I  M
	Report on Communications from
	U  I  T    24
	War Patrol from 2.2.44 to 3.4.44
	I. Message Transmission Service   1. Reception behavior of the switched traffic circuits     A) One-way service from Norddeich Radio:       Switched to from 8.2.44 to 3.4.44       in the area from                               Longitude 100°08'E                                                              Latitude       54°0'N                               To:                                  Longitude  59°45'E                                                              Latitude     35°02S       Receiving conditions in the Program Times from 14.48 - 20.00 hours (DGZ) were good.  No reception by day.  Best wavelengths XXXI and VIII.  All frequencies must be observed throughout, since the reception area for individual wavelengths is often variable.  If, for tactical reasons, the boat was submerged several hours during Program Times, receiving all Radio Messages is no longer possible.             B) Directional transmitter       Switched to like one-way service       In the Program Times 1300, 20.00, and 01.10 hours (DGZ) on wavelengths DFU, DGM and DFF satisfactory reception.  Average volume 3, no reception during the day.  In bad weather or when diving for a long time, it was difficult to puck up all radio messages on this circuit.             C) Radio Circuit Papaya       Switched to from 2.2.44 to 26.8.44 and 1.4.44. to 3.4.44.  In area: Shonan - Penang - Malacca Strait.  Changing, often insufficient volume in the Program Times and for tuning. The best wavelength is B in the program time at 18.00 TZW. Numerous radio and land offices make reception difficult.

Click the flag to view the above page from the original German KTB

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	D) Wavelengths of the DAN [Norddeich] extended Near and Remote service were observed in the area south-east of Madagascar.  On 24 and 36 meters in the period from 18.00 - 02.00 DGZ average Volume 3-4.  Check transmissions were not heard.  36 meters was used as transmitting wavelength
	II.  Excerpt of the Radio Logbook     08.02.44 Departing Penang.  Penang heard on Papaya up to about 90°E, west therefrom communications with Penang uncertain.     18.02.44 Radio Message No. 1 concerning meeting point with "SCHLIEMANN" received.   Boat was submerged off Mauritius. On surfacing the antenna was continually overspilled, as a result reception was limited.  3 Serial Nos. not picked up.     23.02.44 Radio Message Nos. 5 and 6 concerning continued transit to the homeland.  By that Radio Messages 2, 3 and 4 were missing.     25.02.44 In incoming Radio Message the boat was informed: DAN 48 and 49 have Inner No. 4 and 5 instead of 5 and 6.  By that Radio Messages 2 and 3 were missing.     28.02.44 Short Signal sent on 36 meters.  Norddeich was heard with Volume 3.  Short Signal was not picked up by DAN.     29.02.44 18.21 - 18.25 hours calls to Norddeich were not answered.   18.30 hours transmitter failure.  Push button relay out of service, malfunction repaired after 1 hour.   22.10 hours called DAN several times on 24 and 36 meters.  On 36 meters DAN was heard with Volume 3, no check transmitter.   22.55 hours Radio Message transmitted in the blind, no acknowledgment.     01.03.44 08.00 hours sent Radio Message on U-boat Wavelength 6100 Khz.  No answer.   20.43 hours on Wavelength DGM rising and falling tone, Volume 0-4, apparently enemy taking bearing.  Receiver switched off.     02.03.44 01.10 hours Directional transmitter DGM not heard.  Enemy interference Volume 8.  Tone and characteristics as on 1 March.   Thereafter receiver was only switched on by order of the Kommandant.   21.00 hours call to DAN on 24 and 36 meters.  DAN heard with Volume 3.   22.10 hours sent from time group with subsequent Volume request on 8050 Khz (U-boat Wavelength with Serial No. 600-800, Volume 3); no answer.

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	03.03.44 02.50 hours 10 minutes call to "SCHLIEMANN" in accordance with Himati Paragraph 28.  After that at 03.00 hours Radio Message sent in the blind.  Contents: "To SCHLIEMANN": 1.  Have no communications with the homeland.  2.  Suggest new meeting point JB 3889 from 4 March 12.00 MOZ.  3.  Request confirmation on 45 meters.   The radio message was acknowledged after sending:  qsa 4/2 gru ? k k.  On the wavelength there was heavy traffic (BRAKE has not acknowledged this Radio Message).     05.02.44 18.00 hours received Radio Message No. 6.  Request to report position.  18.00 - 20.00 hours called to DAN on 24 and 36 meters.  Attempted to send with new antenna over the extended periscope.  DAN head Volume fluctuating 2-3 sent on U-boat wavelength (Volume 3) no answer.     06.03.44 19.13 hours incoming Radio Message No. 7, new request to report position.     07.03.44 22.00 - 23.00 hours called DAN on call frequency and gap  36 meters.  DAN calls heard at 4, later at Volume 2-3.     08.03.44 After setting off to the east from 18.00 hours noticeably good receiving conditions in comparison with the previous days.  From 18.10 hours called Norddeich on call frequency 36 meters.  Norddeich heard at Volume 4-5.  20.30 hours asked DAN to send Radio Message.  Picked up after two times from DAN.     09.03.44 19.31 hours Incoming Radio Message No. 10, acknowledgment for sent Radio Message and orders to proceed to the east.  19.44 hours incoming Radio Message No. 8 confirming own output on call frequency 36 meters from DAN hear with Volume 3.     10.03.44 19.48 hours incoming Radio Message No. 8 once again a request to report position.  15.14 - 15.48 hours incoming Radio Message Nos. 11 and 12 concerning supply with "BRAKE"     12.03.44 22.30 hours on wavelength DLN with Volume 6 sudden strongly received toneless noise.     13.03.44 19.15 hours incoming Radio Message No. 14:  Communications knowledge.   19.30 hours incoming Radio Message No. 13: Report concerning BRAKE sinking.  Request to report concerning possibility of return transit.  21.51 - 21.55 hours called to DAN on 36 meters.  DAN heard with Volume 4-5.  No answer.  22.02 hours extinguishing spark transmitter with Volume 5 exactly on own gap.  Broke off transmission attempt and dove.     14.03.44 19.50 hours incoming Radio Message No. 15 concerning return transit to the homeland.

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	15.03.44 21.11 hours called to DAN on 36 meters.  DAN heard with Volume 5.  No answer.  21.35 hours on call frequency 36 meters Radio Message sent to DAN.  Repeated by DAN.     16.03.44 02.00 - 02.13 hours incoming Radio Message Nos. 16 and 16 (continued):  Return transit and communications experience.  15.30 hours incoming Radio Message No. 19 concerning meeting with Junker.  16.30 hours incoming Radio Message No. 18 acknowledgment for outbound Radio Message heard by Norddeich with Volume 3.     18.03.44 18.10 hours incoming Radio Message No. 20 concerning fuel take over and engine experience.     22.03.44 16.30 hours incoming Radio Message No. 21 concerning Torpedo attack on Schneewind.     31.03.44 16.46 hours incoming Radio Message No. 22 concerning further use of the boat.     02.04.44 18.36 hours incoming Radio Message No. 23 concerning arrival at objective harbor.

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	Comments of the Command I. The boat was southeast of Madagascar in an area with very bad receiving and transmitting conditions.   Only after setting off in an easterly direction conditions was it better, so that transmitting a message to the homeland was possible.  Sending the Radio Messages was urgent because 1. Radio Messages 2 and 3 were missing and these two Radio Messages were regarded as important in relation to the forthcoming supply.  2. "SCHLIEMANN" was not seen at the supply point and the fastest notification of the homeland seemed necessary.  3.  The boat was not informed of the "BRAKE" operation and other U-boats nearby.     II. If messages had also been sent to the boat on VLF, the periods when the boat had no HF reception would have been bridged for the most part.  Reception of the Program Times would have been ensured if the net deflectors were overspilled and the strong radiation of the two receivers during HF could also have been reduced by VLF reception.  Due to the advantages mentioned first, Radio Message No. 2 and 3 would probably have been picked up despite longer submerged time and bad HF conditions. U-boat VLF was heard in the supply area from 18.00 to 06.00 hours DGZ at Volume 3-4.  HF, on the other hand, only from 13.10 to 20.00 hours. DGZ at Volume 3.               Disadvantages of "Himati" Circuit for U-boats   1.  Command centers in these areas have no experience in U-boat radio, disregard bad weather conditions, longer dive trips and the limited U-boat radio room outfitting and antenna arrangement. Insufficient repetition of Radio Messages.   2.  No instruction on tactical situation in the Indian Ocean.   3.  No transmission of experience Radio Messages, which are extremely important for "Mercator Boats". No radio and limited press reception, therefore no information about war events for a long time.  Filler radio transmissions with only meaningless text, instead of Wehrmacht reports and messages as on U-boat Circuits.   4.  If Radio Messages s are not picked up, there is no check as to whether there is a Radio Message to the boat if there is a long time before the next Radio Message with an internal numbers is received. Radio Messages summarizing U-boat Circuits, about settled Serial Numbers, content Radio Messages and filler Radio Messages.

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	5.  Bad communication on U-boat wavelengths, because U-boats and land stations do not respond to five-digit Radio messages with an internal header.   (Testing by the boats has discovered this.)   6.  Delivery of all messages to the boat by special key jeopardizes key security. Example:  23 Radio Messages were sent to the boat from the homeland using a special key. In addition, the boat radioed home 5 times with a special key.  (Radio Messages were not heard.)  10 identifier groups were available for this traffic, one of which must be used unencrypted at the beginning and end of the Radio Message.   7.  No VLF.           Advantage of U-boat Circuits   1.  Elimination of the above disadvantages.   2.  Communications to home via radio repeater would be possible even in difficult transmitter conditions.   3.  Current information on U-boat situation.           Technical testing of the installation I. 1.  Very strong radiation of the heterodyne receiver.   2.  The transmitter also radiates when the key is not pressed.   3.  All receivers run on battery power.  Very  high consumption on batteries.  New acquisition is not possible here.  Conversion to rectifier operation necessary, but difficult with the means available here.   4.  Engine installation is not suppressed.  [Radio interference from the engine installation]   5.  Unfavorable antenna conditions, only one antenna feed-through of the pressure hull.  Only one antenna for sending and receiving. This means that it is necessary to switch over between transmitting and listening, and it is impossible to switch between listening [receiving on one frequency then another].   6.  Listening gear works poorly and is inaccurate.  Radio Direction finder and depth sounder installations are good.     II. Test with "U-532" at sea showed that the receiver on board radiates very strongly.   "BRAKE" reported that for 4-5 weeks receiver radiation was observed with increasing Volume.   Suspect that it was our receiver.                                                                  Ob.Ltn. z.S. and Kmdt.                             Lt.z.S. and Radio Message Officer

 

	Penang, 5 May 1944
	Supplement to the K.T.B. "UIT 24"   Annex "Report on Communications."
	The assessment of the radio conditions on "UIT 24" during the voyage in the Indian Ocean given in the radio message B 1973 gk from Tokyo does not appear to be correct in all points, given the more detailed documents available here. For clarification, further details are reported below.
	1.)  Receiver and transmitter outfitting:
	The "Mercator"-boats were equipped with a "Marelli"-Short Wave-heterodyne receiver, an all-wave-heterodyne receiver, a "Telefunken"-bearing receiver and a combination Short Wave and Low Frequency transmitter of 1 KW power.
	a)  In terms of volume, the "Marelli" receiver is about the same as the German all-wave receiver, but due to its greater selectivity and the greater amplification required as a result, all the picked up interference and receiver noise come through more strongly, which is disadvantageous at low volumes.  In this sense, the German all-wave receiver is superior to the "Marelli" receiver.  The performance of the large ship Short Wave receiver or even the new "Main" receiver, with which German U-boats are equipped, is of course significantly better.
	b)  The other Italian All-wave heterodyne receiver is slightly worse in terms of performance than the "Marelli" receiver.  Another notable disadvantage of the two Italian receivers is the fact that they work with great selectivity on one sideband and therefore the gap of the received station is hardly or not at all audible.
	Because the two receivers radiate strongly, for this reason alone they can no longer be used.
	c)  The disadvantage of the 1 KW transmitter is that it emits somewhat when the key is not pressed (control transmitter oscillates through, was not keyed).  This superimposition on your own receiver is so strong due to this radiation that reception is no longer possible if the transmitter is on its own and is on the same frequency.  The transmitter and receiver only work on a single antenna, which makes it completely impossible to hear between the two receivers, since both receivers can only be tuned to the gap.  Frequency-precise work is almost impossible.  After taking over the "Mercador"-boats, because no more descriptions and frequency curves were available, new frequency curves would have to be prepared with the help of a LO 6 K receiver, which of course cannot claim to be very accurate.  For this reason alone, even if there had been a receiver for the adjustment of the gaps, working, for example, on deviation frequency was impossible.

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	In the course of the journey on "UIT 24" there were a few failures on this transmitter, which could not be fixed in all cases with on-board means.  For example, it was not possible to work with full anode voltage because the transmitter would then emit a continuous wave. Therefore the transmitter had to be operated with a lower voltage.  In addition, the transmitter could no longer be tuned correctly, the antenna ampere meter deflected fully, while the ampere meters of the preamps hardly deflected.
	d)  The "Mercator"-boats only have one antenna. This antenna is very long, it leads from the forward antenna support on the forecastle on both sides of the tower to the aft antenna support.  Thus unusually long antenna may be the reason for the unfavorable Short Wave performance.
	e)  Reception was also severely affected by the fact that the entire electrical system is not suppressed.  Every fan, every electric motor, even every increase in speed could be heard in the receiver.  All receivers, including the depth sounder and the listening installation, have so far been working exclusively on battery power.  Since no new batteries can be procured and the power supply of these devices has to be converted to rectifier operation, the faults were even more clearly noticeable.  Interference suppression of the entire electrical system is therefore absolutely necessary.  Most of this has already been carried out on "UIT-26" (Striegler).
	2.)  Reception conditions submerged:
	During the entire voyage, the homeland could only be heard between 13.10 and 20.00 hours DGZ.  With good weather conditions, only the Program Times 13.10 hours DGZ on DFU and 14.46 hours DGZ on the one-sided service from Norddeich could be recorded with certainty.  All other Program Times were observed, but mostly with insufficient volume.  During the day there was no reception at all.  The Very Low Frequency of the U-boat Circuits were significantly better, about from 1800 - 06.00 hours DGZ heard with sufficient Volume.  In several cases, the announcement of new radio messages was detected at the beginning of the Program Time, but the radio messages themselves could not be picked up because of the falling Volume. The check transmitters from Norddeich were not heard once during the entire voyage.
	In addition to the electrical interference on board, reception conditions in bad weather areas were impaired by strong atmospheric disturbances.  Due to bad weather, the boat often had to dive to avoid further sea damage and the reception was completely lost for the time of the submerged cruise.  When surfaced, the net deflector was constantly being overspilled by rough seas and swells. The boat is significantly wetter than German boats, which was clearly determined during a together transit with U-"Junker".

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	3.) Repetition Program:   The planned surface ship Repetition Program on the wavelengths of the direction transmitter and from Norddeich were not sufficient.   A few examples:   a) Radio Message Serial No. 79 Inner No, 1     17 February announced at 19.10 hours on directional transmitter, not picked up in the rest of the Program Times.     18 February picked up on directional transmitter at 19.10 hours.     Announced on Single Side Service, not picked up.  Otherwise not heard.   b) Radio Message Serial No. 48, Inner No. 5     23 February picked up on Single Side Service.  Only heard in this single Program Time.   c) Serial No. 5     20 February picked up on directional transmitter at 19.10 hours, otherwise not heard.   d) Radio Message Serial No. 39, Inner No. 13     After own request to the homeland Radio Messages were repeated often.     12 March picked up on Single Side Service at 1849 hours.     13 March Radio Message was heard once again on Single Side Service at 18.48 hours.       Four Serial Numbers were not picked up in the period from 18 - 21 February, when the boat proceeded submerged for a long time due to a hurricane.  In these missing Serial Numbers were the Inner Numbers 2 and 3. The announcement of the radio message with the Inner Number 3 was also heard, as was determined from the routing number after arrival, but the radio message itself was not picked up within the Program Time because the Volume was too low. The missing of Internal Numbers 2 and 3 was first determined after receiving the radio message with the Inner Number 4. On U-boat Circuits the not picking up radio messages becomes known much earlier, since the homeland often announced the unimportant routing numbers (Kam.-reports, Wehrmacht Reports etc.).       4.) Utilization of all transmission possibilities:           Through the radio messages with the Inner Numbers 4 and 5 from 23 February it was found that Inner Numbers 2 and 3 were missing and that the homeland assumed the boat had already been supplied and was on its way home.  Nevertheless, the boat remained at the waiting station for a few days, but "SCHLIEMANN" was not found here. Now it was assumed that the Inner Numbers 2 and 3 contained a new meeting place and a Short Signal was sent to the homeland that was not heard despite being sent twice.  Since the fuel supply was getting tight, all means were tried to send a message.

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	Since the delivery of radio messages in the gap of the Norddeich wavelengths remained unsuccessful, and since it was known that working on a precise frequency was very difficult, an attempt was made to establish communications with Norddeich on the call frequency.  No enemy call signs were used for the call, but the secret call signs in accordance with "Himati" Appendix 4 No. B 3.  The use of these call signs was not correct, but it shouldn't have interfered with getting through to home.  When no communications were achieved by this either, in two cases a radio message was sent on U-boat wavelengths, which could be heard well, but without success either.  In addition, a radio message was sent to "SCHLIEMANN" on March 3 in accordance with "Himati" Paragraph 28. During the whole period of these transmissions, i.e. in the period from 28 February - 7 March reception conditions on the wavelengths of the extended local and long-distance service from Norddeich were noticeably poor.  Presumably, these poor receiving conditions were partly due to the location.  Attempts to receive and transmit with a new antenna attached to the extended periscope resulted in slightly better reception, but it was still not possible to achieve communications with home. Only when the boat had moved further to the east did the Volume become louder in the course of 8 March suddenly rising to 4, later even to 5.  Only now did the boat get in touch with the homeland again.
	When a radio message was sent on a U-boat Circuit, the homeland interrupted its program until the radio message was properly delivered.  It was sent in the interval between two radio messages transmitted from home.  There was no acknowledgment.
	After the return, the Italian Radio Master Soehnal, who recently came with the same boat from France to East Asia and belongs to the now own shipyard command in Shonan, came the statement that the Italian boats used to work on the call frequency with Rome or Bordeaux, especially when it was necessary to get through.  They were also familiar with working in the gap.  He also said that he had always worked with over 3000 volts of anode voltage.
	5.)  Summary:
	In summary, it can be said that the poor reception conditions can be attributed primarily to poor receiver equipment and poor antennas, and on the other hand due to the location and atmospheric disturbances caused by bad weather.  Due to longer submerged cruises, reception was sometimes completely lost. If VLF reception had also been possible, messages could have been picked up in this way at certain times of the day.  If the boat had been completely on a U-boat Circuit, it would have been able to get a better picture of the situation and possibly, without radioing, could have approached a meeting point for "BRAKE" - combat boats.  Transmission difficulties were based on the fact that the transmitter was not completely operable and it was not possible to work on the correct frequency using the "Marelli receiver".
	An attempt will be made to rectify the deficiencies that have arisen as a result of this voyage as far as possible before "UIT-24" and "UIT-26" leave. "UIT-24" still has to be provided with a good receiver, the transmitter has to be thoroughly overhauled, and tests have to be carried out with more favorable antennas.

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	6.)  Key security:
	The enemy B-Dienst (as does the German) works with information and working methods that can hardly be overlooked from the point of view of the U-boat service.  Therefore, it seems wise to be overly cautious about key security rather than just sticking firmly to the paragraphs of the Radio Instructions.  In addition, Paragraph 7 of the "Tibet" key regulations cannot be reconciled with the frequent use of special key identification groups.
	It can be assumed with certainty that the enemy B-Dienst, monitoring the wavelengths of the overseas service, found important clues solely on the basis of the constantly recurring, unencrypted identification groups.  For about a year now, all messages to blockade runners and suppliers, with the exception of Kam.-reports, have been encrypted using a special key.  Based on the constantly recurring unencrypted identification groups, a list of identification groups could be drawn up through ongoing observation.  The affiliation of a group of identification groups to a specific command could be determined by radio messages with the same content being sent to different commands at about the same time, i.e. identification groups of different affiliation groups appearing in these radio messages at about the same time.  This finding was made even easier by the fact that an identifier group pair related to a radio message is pulled apart in the case of another radio message and an identifier group of this identifier group pair is combined with another identifier group to form a new pair.  With these two radio messages, you can see the affiliation of three identification groups to a specific command.  The beginning of the occurrence of such characteristic groups allows conclusions to be drawn about the departure date. If some departure dates have also become known through hostile agent reports, the rest can already be ascertained from these observations. Since the number of identification groups for the general "Tibet" procedure is significantly greater than that for the special key procedure, these identification groups do not appear significantly in the external radio picture.
	All in all, this would give a very clear picture. If, after these departure dates, the enemy plots, the approximate location of each ship should be indicated at any time.  Since this key procedure has been in operation for many months, it must be assumed that the enemy. B-Dienst has been trying to evaluate this fact for itself for a long time and at the moment has considerable information on the basis of its ongoing observations, which may have been valuable support for the enemy in the approach to our blockade runners and suppliers.
	Which results of the enemy B-Dienst can also still draw from this procedure, can perhaps only be judged by an experienced B-Dienst man.
	The key security itself is not at risk as a result. However, since it must be assumed that fragments of key information have become known to the enemy due to various circumstances over the years, any further negligence, e.g. the use of the same identification groups for different radio messages, is ruled out, even if these radio messages are days apart for the enemy B-Dienst a fact that at least makes it easier for him to crack our radio messages.
	signed in draft  Bartsch
	Oblt.(NT) and NTR Südraum