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IN THE LATE 1960s - EARLY 1970s

(The radio equipment and communication technologies described below are no longer in use today)

(The equipment has been declassified and can be found on eBay from time to time)

The KL-7 crypto machine

The KL-7 crypto machine was used to manually encrypt and decrypt classified messages sent and receive by morse code. Plain language was encrypted into 5-letter groups for CW transmission. The reverse was done at the receiving end. Received 5-letter groups were fed into the KL-7 and plain language text came out on a rolling tape.


The KWR-37 crypto machine

The KWR-37 crypto machine was an in-line crypto machine for teletype radio traffic. When transmitting, plain language messages were typed on a Model 28 teletype machine. The output from the teletype machine in baudot code was fed into the KWR-37. The encrypted text coming out of the KWR-37 was fed into a transmitter and transmitted in FSK code. When receiving teletype traffic, the process was reversed and plain language appeared on the teletype machine. Time synchronisation was critical for the KWR-37 to decrypt what had been encrypted by another KWR-37 machine. Crypto codes were changed daily at 0000 Zulu by replacing a perforated card. The horizontal door on the front of the KWR-37 indicates where the perforated card was located.



The AN/URC 32 MF-HF transmitter was a beast. Around 6 feet tall. The frequency coverage was 2 to 30 MHz and power input into the final was 500 watts.


Modes included

A1 (CW telegraphy), A3a (SSB reduced carrier), A3b (two independent side bands, reduced carrier).


A9 (Composite transmission), A9a (SSB full carrier transmit) and  F1 (frequency shift telegraphy for teletype transmissions).


The main use of the URC 32 was to transmit teletype messages in F1 mode.


The URC-32 was also used for long distance voice transmissions and phone patches on the HF band. Although it could also be used to transmit morse code the Radiomen preferred to use the 618T transceiver for CW. The 618T was the preferred morse code CW transceiver because it was easier and faster to tune or change frequency.



The AN/ARC 618T MF-HF transceiver was designed for use onboard aircraft. It was used in submarines because aircraft and submarines have limited space.


There were two 618T transceivers onboard. Frequency coverage was from 2 to 30 MHz. In the image above, the transceiver is on top and the remote control unit on the bottom. The remote control unit was located near the radio operator sending traffic, making it easy to tune and change frequencies. Because it was easy and quick to tune, the 618T was the preferred transceiver for CW morse code transmissions. Time was of the essence when the submarine came up to periscope depth to transmit radio traffic.



The AN/ARC 552 VHF-UHF transceiver was also designed for use onboard aircraft. It was ideal for use in submarines due to limited space.


There were two AN/ARC 552 transceivers onboard. It's most common use was to communicate with aircrafts and ships nearby during exercises at sea. Radiomen kept control over the equipment but the operators were mostly the officers in the control room.



There were two AN/URR 502A receivers in the radio room onboard submarines. They were the main multipurpose HF receivers. The unit was made up of the URR 501 (Racal 17) receiver covering from 980 kHz to 30 MHz. It was also made up of the CV5046 Low Frequency Converter to cover from 10 kHz to 980 kHz.



Used to send and receive radio teletype (FSK) at 100 words per minute. The signals were encrypted with the KWR-37 crypto machine. Incoming messages were simply ripped off and put on pads for distribution to the Captain or other officers. Outgoing messages were prepared in advance using the perforator seen in the little window to the left of the keyboard. Baudot tapes were created. When it was time to transmit, the prepared baudot tapes were used to transmit at 100 words per minute. In ship-to-ship communication at sea, transmissions were done manually using the keyboard. In this case, speed was depending on the typing speed of the operator.



This VLF receiver was used to copy VLF broadcast when submerged. The CV 5046 also mentioned above could be used to copy VLF broadcast. Frequency range was from 14 to 22.5 kHz. Broadcasts were copied on 17 and 21 kHz. VLF antennas included the ALK in the buoy, the ALM in the fin or the ALW floating wire.


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Surface ships were able to copy the Navy's main radio broadcast continuously on a 24-hour basis. However, for a submarine to copy the Navy's main radio broadcast, he had to be on the surface or at periscope depth with the radio mast raised above the surface. Most of the time, submarines could not copy the radio broadcast because they were submerged below periscope depth. Therefore submarine radio traffic using morse code was sent during specific submarine schedules every four hours. It was up to the submarine Captain to decide when to go up to receive radio traffic. Depending on the operational exercise, he sometimes decided to wait for the next schedule thus taking the risk of missing messages adressed to the submarine. Each message to submarines had a serial number and was sent on four separate submarine schedules. So up to three schedules could be missed without missing any messages. Sometimes, four or five schedules were missed due to operational requirements but it was still OK if there had been no new messages on the first two missed schedules. However, there were messages being missed on occasions and a request had to be sent to the shore station to have the missed messages resent again. When this happened, the missed messages were sent again on the next four schedules.


Every 4 hours, the radio sparker on duty reported to the control room that the next radio schedule was coming up in 30 minutes. If it was decided to go up and copy the radio traffic, the radio sparker got ready by tuning his receiver in advance and preparing the tape recorder. As soon as the submarine arrived at periscope depth, the radio mast was raised and the radio sparker did the final tuning of his receiver.


When it was time to begin the submarine radio schedule, surface ship radio traffic being sent at 22 words per minute was stopped by the shore station. Submarine radio traffic would then begin in morse code at 100 words per minute. When submarine radio traffic was over, the shore station returned the navy's main radio broadcast to surface ship radio traffic at 22 words per minute.


A tape recorder similar to the one above was used onboard submarines to record the submarine morse code radio traffic at 100 words per minute. When all submarine radio traffic had been recorded the submarine would quickly return below periscope depth.


After the submarine had returned to the deep, Radiomen lowered the speed of the tape recorder to copy the messages. Morse code recorded at 100 words per minute was reduced to 25 words per minute for easy copying on a typewriter. It was important to record the CW signal at high pitch. It made it easier to copy the messages because the slower speed drastically reduced the pitch.


It should be noted that most radio traffic was classified and had to be encrypted. An in-line crypto machine, the KWR-37 mentioned earlier, was used for radioteletype traffic, but morse code traffic was a lot more work since it had to be manually encrypted into 5-letter groups and decrypted back into plain language using the KL-7 crypto machine. It was a lot more work for radiomen, and a lot slower process.


The Aldis Lamp

This portable Aldis Lamp was used to communicate with ships and other submarines within a visual distance. It was very useful when under "radio silence". Radiomen on surface ships did not use the lamp and did not practice morse code by light because morse code by light and semaphore by flags was done by Signalmen. There were no Signalmen on submarines so the Radiomen had to use the Aldis when required.


The photo above shows PO2RM Bill MacDonald using the Aldis Lamp while at sea. It should be noted that Signalmen in the Navy were not the same as Signalmen in the Army. A Signalman in the Army is actually the same as a Radioman in the Navy. A Signalman in the Navy deals only with visual communications (light, flags and semaphore) (no radio).


The AN/WQC-2 Underwater Telephone

(also known as Gertrude)

The above photo is the control panel for Gertrude. Used to transmit and receive voice or an audio tone under water. The signal is heterodyned to a high pitch for acoustic transmission through water.


Transmit acoustic waves in the range of 300 Hz to 3 kHz. Used for ship to ship, submarine to ship, ship to submarine and submarine to submarine communications.


Provides unsecure communications because signals are not encrypted.