Spies, clandestine operators, as well as soldiers in the field used burst encoders to record and send brief messages at a very high rate of transmission to avoid enemy detection. Inside the recorder is a rotating disc with permanent magnets that act as a recording head similar to the head of a tape recorder. The head is protected by a metal lid that can easily be removed. Inside the lid is a small stylus that is used by the operator to enter numbers using the dial.
After unpacking the magnetic tape cassette from its field pouch, it would then be attached to the recorder. The operator then used the stylus pen to enter the pre-coded message as a series of numbers (0-9). The stylus was inserted into the corresponding hole in the dial and then used to rotate the dial until the pen was blocked by a small metal bracket. The stylus was then pulled out so that the dial could return to its default position in exactly the same manner as an old-style telephone.
As the dial was returning to the default position, the metal tape was advanced slightly and a digital coded number was recorded on the tape by the rotating permanent magnets inside the recorder. The advantage of this system is that it requires no batteries. The predecessor to this burst encoder was the R-350 which used a photo film roll.
In practice the recorder and multiple cassettes would often be issued with each radio set. A secret agent would use the dial to record numbers corresponding to pre-coded messages onto the tape. He or she would then hide the tape in a pre-determined place, a so-called dead drop, where he would find a new blank tape.
The tape was picked up later by the radio operator who would take it to the secret radio station and attach it to the R-353 transmitter. After establishing contact with the East-European head office, the message would then automatically be transmitted at very high speed (burst) to minimize the risk of detection.
The advantage of using a dead drop was that agent and radio operator didn't have to be acquainted, minimizing the risk of compromise if one of them was exposed. In certain situations, the R-353 was also used directly by agents themselves to send messages home.
Only digits are recorded by the R-353 burst encoder and the digits were associated with preselected coded messages. Thus, the small cassette could safely be left in a dead drop. Even if the cassette were to be compromised, the coded message would still be secure.
The R-353 was in use in many Eastern European countries from the early 1960s well into the 1970s and was captured by western agencies on a few occasions. One documented event was the capture of an East-German agent in The Netherlands in the early 1960s. When he was finally exposed, the Dutch security agency BVD (now AIVD) found a fully operational R-353 in his home
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