Kurier system
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Kurier was a burst transmission system for U-boat communications that was first sea trialed by the Kriegsmarine in 1943[1] and subsequently fitted to the Type XXI submarine.[2]: 103–104 Having learned of the success of the UK's "huff-duff" systems in rapidly locating radio transmissions, Kurier was developed to dramatically reduce message transmission times from a typical 20 seconds to about 250 ms, and never longer than 450 ms (just under ½ a second). Due to the deteriorating position of Germany by that time, Kurier never became operationally effective before the war ended.
Prior to the opening of World War II, the German Kriegsmarine developed a system known as kurzsignale for sending radio signals from U-boats back to headquarters. At the time, it was possible to measure the bearing of a radio transmitter using a system known as a Bellini–Tosi direction finder (B-T). A trained B-T operator could produce a reasonably accurate measurement in about a minute. To prevent this, kurzsignale encoded the message into a series of short codes that could be sent by a competent radio operator in about 20 seconds.[3] While this could still be intercepted by a B-T operator, it would require considerable amounts of luck, and the resulting measurement would be inaccurate.
Unknown to the Kriegsmarine, Robert Watson-Watt had developed a new system known as huff-duff that could take such measurements in a fraction of a second. He had originally developed the concept to allow the Met Office to measure the fleeting signals from lightning, and had used it to provide thunderstorm warnings to pilots. Despite the system being publicly shown, even featured in newsreel films, the concept was largely ignored outside the UK and development continued in secret. It is estimated that 24% of all U-boat sinkings were due in part to huff-duff intercepts.[4]
In the spring of 1943, Dr. Bendt of Telefunken came up with the Kurier concept. The first prototype was constructed under the direction of Baurat Vollmeyer, a Kriegsmarine official, and test messages were sent from Holzkirchen in southern Germany[a] to Dannau, near Oldenburg on the Baltic coast. Having proved the concept, the team moved the receiver to Bernau outside Berlin for further testing. An improved model was available in early 1944, and tests were carried out on board a U-boat. These revealed the previously unseen problem that the electric motor driving the system, taken from a windshield wiper, changed its speed based on the temperature and humidity, which were very different on a U-boat. This was addressed by replacing it with a synchronous motor that accurately maintained the proper speed.[5]
The final version was not available until early 1945, late in the war. A total of four sets are known to have been fit to U-boats in Kiel. By this time the Soviet forces had reached Kuestrin and Bernau was evacuated. A new receiver station was set up on 27 April in Bokel, north of Hamburg.[5] The war ended days later.