Radio Communications of German U-boats in WWI and WWII

by Robert Derencin


Very soon after the invention of radio communications, many countries were established radio communications services in theirs naval forces. First communication devices were very simple, distances between radio stations were short, but even that, radio was useful. The first application of radio in combat was in the war between Russia and Japan, in 1904. During the blockade of Port Arthur, the Japanese fleet was commanded from the Navy base distanced 110 km from the Port Arthur. In the battle of Tsushima, Japanese reconnaissance ships reported movements of Russian fleet by means of radio…


In the World War the First all main Navies involved in war had relatively good radio services. Of course, the equipment were simple, radio personal was without experience, but by the time, things getting better. The most often frequency bands for the naval communications were Low frequency and Medium frequency bands. The submarines were using (those days) just the Low frequency band. Like always, when one "weapon" is invented, there is very soon something against the "weapon". In Russian-Japanese war, both sides were intercepting radio communications of the opposite side. It was radio reconnaissance. In the WW1 radio-intelligence was consisted of the radio reconnaissance and direction finder services. By means of that, the opposite side was able to know where enemy ships were, and what messages they changed. Because of that ships frequently used to communicate by receptions. It mean that until the contact with the enemy, they just received messages.

When the contact was established, they transmitted message about that. Until the contact with the enemy, submarines rarely used their transmitters. If they sent any messages from the submarines, the messages were short and always coded (i.e. ciphered). Submarines communicated with their bases and with another submarines on the Low frequency band, just by night, on the surface. The submarines communicated by night because there always was danger to be sighted from the enemy ships or aircraft.


After the WW1, German navy was very reduced. The navy was consisted of few old battleships and smaller units. German navy was not approved to has any submarine. Of course, like on another fields of armed forces, German navy leadership found way to keep informed and qualified for the newest submarine technology. German navy engineers and submariners constructed and "tested" submarines in another countries (e.g. Finland, Soviet union…). There was "antisubmarine course" on the Baltic sea, where German navy "anti-submarine forces" trained for the "faith against submarines", etc. Normally, between WW1 and WW2 there were many improvements of radio communications. From 1926 ships were equipped with High frequency (HF) radio equipment. Because of that, distance between stations could be longer, antennas of the HF radio-stations were smaller and, after all, communications were better.

From 1930 ships were equipped with radio-telephony radio stations. Before 1930 the ships were had just radio-telegraphy radio stations. That was big improvement of radio communication at all. From 1933 German navy started to grow up, they built more and more (better and better) submarines. No doubt that the German navy was able for the next step…


WW2 was war of industry and science between the enemies. There is no doubt that Germans had strong industry and excellent scientists and engineers, but Germany was blockaded and during the war they had more and more problems. One big problem was Nazi government. Instead of that, Allies had not such problems, and as times passed, the Allies made more and more improvements of weapons and electronics. Allies broke Enigma cipher code and they were able to read almost all messages ciphered by the Enigma.

Also, the Allies had chain of direction finders stations, so they were able to find position of German radio stations (including the positions of German submarines). Then, the Allies improved radar equipment and ASDIC. All that was the most important in war against the German submarines. Before the war, German navy leadership planned that the submarines would operate alone until reception information of enemy ships or convoy movements. But, if you need information and if you somewhere on Atlantic, you must use radio. When the submarines used their radios, the Allies was able to get all, the information, position of the submarine, future movement of the submarine… And normally, as the time passing the German submarines had more and more poorly chance to survive. When the Allies air crafts were equipped with the radar and direction finder units, it was end for the German submarines.

During the WW2 German navy submarine crews were showed high level of skills, they had excellent training and they were motivated. Radio personal was excellent, too. But they were not informed enough about "new war", electronic war. With the time, they realized that when they use radio the Allies destroyers and aircraft "somewhat" knew their position. They realized even that in state of poor visibility or by night, they could be found and attacked. But they believed that the Enigma was enough strong to keep safety of their communications. And they were wrong.

All above mentioned mean that the German submarines had not conditions to win in WW2.


French scientists started researching of underwater radio communications in 1917. Head of researching was French scientist Broji. They found that some radio waves partly penetrate into water. They used radio frequencies from 15 kHz to 33,3 kHz. (Very Low Frequency band, VLF). With the strong powered radio signals they succeeded to communicate from a distance of 16 nautical miles, depth of submarine's antenna was 10 metres.


After the WW1 scientists continued researching of underwater radio communication. They made possible "one way" underwater communication between land radio station and submerged submarine, if antenna of the submarine was deep up to 10 to 20 metres from sea surface. The "one way" communication means that the land station could transmit messages to the submarine, and the submarine was able just to receive the messages. The submarine was not able to transmit messages to the land station. Two main reasons for "one way" communication were if you communicate on frequencies of Very Low Frequency band (VLF) you need very long wire antenna and transmitter able to generate strong powered radio wave. Submarines had not enough length for the VLF antenna. Also, the submarines had not enough strong power supply for VLF transmitters.

Depth of submerged submarine (i.e. submarine's antenna) for sufficient underwater radio communication depended about distance between land radio station and the submarine, power of radio signal, frequency used in the communication and salinity of the sea water. Before the WW2 German submarines had underwater radio communication with land stations on VLF band, on frequencies from 15 kHz to 33 kHz.


From 1939 to 1943 main German navy radio transmitter for the underwater radio communication was "Nauen". The "Nauen" worked on two frequencies:
3. 23 kHz, power 200 kW, and
4. 16,5 kHz, power 300 kW.

From 1943 to the end of WW2 main radio transmitter for underwater radio communications was "Goliath". The "Goliath" transmitter worked on frequencies between 15 kHz to 25 kHz. Power of the "Goliath" transmitter was 1800 kW. The "Goliath" was able to communicate with German submarines everywhere except when the submarines were positioned in deep Norwegian fjords. Table number 1 shows communication possibilities of the "Goliath", depended about distances between the "Goliath" and particular submarines.

Table number 1:

Position of submarineDistance from "Goliath" (in km) Depth of submarine's antenna (in metres)
North sea1000 km14 - 24 m
Mediterranean sea2300 km12 - 17 m
Bay of Biscay up to 30 m
Indian ocean6000 - 8000 km7 - 14 m

During the WW2 underwater radio communication was very useful. Submarines were able to receive messages from their commands without surfacing, i.e. the submarines could been submerged. The submarines could not be detected by radar, and the Allies' direction finders could not detect submarines' positions because the submarines were not using their radio transmitters, just receivers. But because of the "one way" communication, it was specific organized traffic, by previously determined scheme.

Messages were marked by serial numbers, each serial number for the each submarine. The messages were transmitted without confirmation of reception, mostly by night, sometimes from the few transmitters simultaneously. Submarine knew time of transmitting, when the time was coming, the submarine was on right depth, and radio operators were monitoring the radio transmitter with best power of radio signal. Efficiency of reception was 90%. It means that 90% of all messages were received successfully. It was very good, indeed.


There were many improvements of radio communications and underwater radio communications in WW1 and WW2. By the time, all navies improved their communications. German navy had good radio service, too. They ensured good change of information between the Navy command and the submarines. But, they believed that Enigma cipher machine is enough capable to ensure safety of their messages, and they were wrong. It was one of reasons why Germans lost a "battle for the Atlantic" against the Allies. Despite reason for what German submarine's crew members fought for, they were good trained and motivated, and they did their best.

Table number 2 shows frequency bands used for radio communications and underwater radio communications in WW1 and WW2.

Table number 2:

Name of Frequency band AbbreviationWave length
(in metres)
(in kHz)
Very Low FrequencyVLF100 000 - 10 000 m 3 - 30 kHz
Low FrequencyLF10 000 - 1 000 m30 - 300 kHz
Medium FrequencyMF1 000 - 100 m300 - 3 000 kHz
High Frequency HF 100 - 10 m 3 000 - 30 000 kHz

This article was published on 7 Apr 2002.

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Erikoismiehet Iskevat. Karhunen, Joppe, 1971.
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German Naval Code Breakers. Jak P Mallmann Showell, 2003.
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The War Diaries of U-764. Guske, Heinz F. K., 1996.

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