- German air force Elektra-sonnen
- D/F-ing of very low frequency shore transmitters
- Navigation for "Total Underwater Warfare"
Elektra-sonne Facilities (as of May 1944)
1. SummaryThe most important new development in navigation during the war was the use of German air force (GAF) Elektra-sonnen for U-boat navigation. The use of beamed signals from these transmitters enabled U-boats to fix their position by employing only an ordinary radio receiver. A great deal of attention was given by COMSUBs to amassing information on the adequacy of navigation by this means. The results of experiments were not directly available to radio intelligence because they were included in the written communications reports of the U-boats, but there were several instances in which successful navigation by Elektra-sonne was claimed. It was found that this method was available to U-boats making long submerged cruises, as Elektra-sonne signals could be received over the Schnorchel round dipole. An experimental program to determine the possibilities of D/F-ing very low frequency transmitters for navigational purposes was also carried out, but no significant results were recorded in radio traffic.
The concept of "Total Underwater Warfare" brought about increased emphasis on all methods of navigation which could be substituted for the taking of astronomical fixes. Navigation in coastal waters was a matter of particular concern because of costly accidents to U-boats due to faulty navigation. Accurate dead reckoning, terrestrial navigation, and utilization of lines of sounding were recommended for their reliability; but the exercise of appropriate caution was urged as the basic principle in coastal navigation.
2. German air force Elektra-sonnenThe most important development of the U-boat war in the field of navigation was the utilization of GAF Elektra-sonnen. The experimental observation of Elektra-sonnen as an aid to U-boat navigation was begun by boats in the Bay of Biscay in April 1943 and later extended to other more distant areas of the Atlantic. The Elektra-sonnen in use by U-boats at various times were located in Norway, Holland, France, Spain and the Danzig area. Ranges of the beacons varied, the longest range cited in traffic being that of Sonne 6, up to 1300 miles.
The advantage of navigation by Elektra-sonnen lay in the fact that in addition to the opportunity for D/F-ing offered by an ordinary radio beacon, their transmission of beamed signals, turning gradually past definite sectors, made possible the fixing of definite direction line by use of an ordinary radio receiver. Accurate bearings could be obtained by a process of counting or timing dots and dashes of the beamed signals and plotting the result on charts especially prepared for Elektra-sonnen navigation. Full details of this procedure were given in an operation manual found aboard the captured U-505 in June 1944.
As was usual with newly introduced procedures and equipment, the U-boat command experienced considerable difficulty in assembling necessary information from practical experience because of inadequate reports from U-boats. There was no evidence in 1943 that any satisfactory amount of information had been reported, and as time went on the demand for greater use of Elektra-sonne grew more insistent. On 22 March 1944 encouragement was offered in a message form COMSUBs in which he stated:
Recent experiences have shown that after repeated practice in navigating by Elektra-sonne very good results were obtained. Work with it as often as possible, particularly in the North Atlantic. (1653/22 March 1944)
A few days later the U-boats were told:
Navigation by Elektra-sonne had not been tested fully enough in the past. U-boats have used the sonnen almost exclusively just for taking bearings and thus have yielded insufficient results. The advantage of the sonnen is that positions may be ascertained without D/F set. (1850/31 March 1944)
The long submerged periods which resulted form increasingly extensive use of Schnorchel late in 1944 accentuated the importance of any aid to underwater navigation, and use of Elektra-sonnen for this purpose was advised in experience message 181 (1917/6 November 1944) in the following terms:
The commanders still devote too little attention to navigation by Elektra-sonne. Good navigation is possible even when submerged. There have been many favorable experiences. For practice you should navigate by Elektra-sonnen all the time, even if there is another fix available, There is thus a means of comparison. The commander will have to justify failure to use Elektra-sonnen.
Submerged U-boats were able to hear Elektra-sonne signals over the Schnorchel round dipole, while transmission could be heard over the D/F loop if it was out of the water.
The extent to which navigation by Elektra-sonne had been developed by the closing months of the war was indicated by a message stating:
One U-boat returning from mid-Atlantic had a correction form estimated position of only 2 nautical miles on entering port after a 4 weeks passage without taking position by star sights. Navigation by Elektra-sonnen only. In addition a running fix outside the port of destination was taken form Sonne 8.(1819/31 January 1945).
3. D/F-ing of very low frequency shore transmittersOn 21 January 1944 (1520/21 ff) an experimental program to determine the possibilities of long-range D/F-ing of very low frequency transmitters for navigational purposes was announced. Bearings were to be taken as frequently as possible on specified transmitters on both sides of the Atlantic with a view to determine the maximum range for sufficiently accurate bearings and the possibility of taking cross-bearings on American and European transmitters in the middle of the Atlantic. Comparison was to be made with dead reckoning or astronomical fixes, and full details, with evaluation exclusively by the U-boat commander, to be included in the boat's communication report. Because of the fact that all data were to be handed in after returning to port, it was impossible to determine by radio intelligence what the results of the experiments were. The only indication was a statement in a situation reports on the Minch area that approximate bearings
had been obtained on the Rugby very low frequency transmitters.1 (1927/27 December 1944)
4. Navigation for "Total Underwater Warfare"The attempt at "Total Underwater Warfare", which was foremost in the plans of the U-boat command at the end of 1944, brought with it considerable concern over improvement of navigation during long submerged periods. One group of series of "General Rules for Total Underwater War" directed U-boats to:
Avoid surfacing for astronomical fix as far as possible. Keep scrupulously exact dead reckoning, allowing for current. Use of sounding apparatus, Elektra-sonnen and radio beacons makes a thoroughly exact determination of position possible, according to available experiences. Make use of every possibility for determining positions by landmarks when near our own and enemy coasts. (2040/16 November 1944)
The "available experiences" presumably included some which had been mentioned earlier in the same month. Speaking of accurate fixes which could be obtained from lines of sounding taken by repeated crossing of prominent depth demarcations in various directions, COMSUBs had reported:
Förster (U-480), coming form the Atlantic after an 18-day cruise without fix, made an exact determination of position by this procedure and without any further navigational aid reached the escort pick-up point. Von Friedeburg (U-155) made his way in form Iceland passage guided by the Elektra-sonne equisignal sonne beam, then reached the escort pick-up point without difficulty by means of soundings. (2239/2 November 1944)
A new aid to sounding in the form of sonic telegraphy was also recommended on the basis of experiences of Schimmelpfennig (U-1004), who measured depths of over 1000 meters by
sending out sound by sonar and timing the interval before return of the echo. (2005/3 November 1944) That there need for particular attention to the problems of navigation coastal waters was evidenced by two messages of 24 December 1944, which placed great emphasis on caution in such waters One of the messages called attention to collisions between boats and other German vessels resulting form lack of navigational practice. (1908/24 December 1944) The other summed up the desired navigational policy as follows:
Since astronomical reckonings are not to be carried out in enemy coastal regions, the greatest value and extreme care must be put on very plentiful terrestrial navigation, painstaking dead reckoning with considerable of current according to current atlas, and utilization of soundings (line of soundings). As a basic principle, if position cannot be obtained beyond doubt, always assume that the U-boat is in as unfavorable a position as possible, and act with appropriate caution in waters dangerous for navigation. (1156/1443/24 December 1944).
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1. Rugby transmitters were used for the Broadcasts to Allied Merchant Ships (BAMS).