Thetis was the name of a floating radar decoy used by German U-boats during the Second World War.
Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the object(s). Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed.
U-boat is an anglicised version of the German word U-Boot[ˈuːboːt](
The device was stored dismantled in the bow compartment as a pole about two metres long. Assembly usually took place in the U-boat's conning tower, and could be assembled in about four minutes (FuMT 2 - Thetis IIC). Later versions could be launched from a standard torpedo tube (FuMT 4 - Thetis US). When deployed, it was extended to a total length of eight metres, half of which was submerged. The upper half had a series of reflectors that were tuned to Allied anti-submarine radar wavelengths to give the same return signal as a U-boat. The number of Thetis decoys carried varied between different U-boats:
The Allies of World War II, called the United Nations from the 1 January 1942 declaration, were the countries that together opposed the Axis powers during the Second World War (1939–1945). The Allies promoted the alliance as a means to control German, Japanese and Italian aggression.
- U-66 carried approximately 12 units during her 10th and last patrol between 16 January 1944 and 6 May; all were used in the Bay of Biscay. [1]
- U-91 carried 16 units during her 6th and last patrol between 25 January 1944 and 25 February. [2]
- U-371 carried an unknown number of units during her 21st and last patrol between 23 April 1944 and 4 May. [3]
- U-575 carried 15 units during her 13th and last patrol between 29 February 1944 and 13 March. U-575 would surface every night and laid a total of 10 on her outward voyage, the remaining units were to have been laid in the same area on her return. [4]
- U-744 carried 20 units during her 2nd and last patrol between 24 February 1944 and 6 March. U-744 used them on her outward voyage between 11°W and 12°W in the Bay of Biscay. [2]
German submarine U-66 was a Type IXC U-boat of Nazi Germany's Kriegsmarine during World War II. The submarine was laid down on 20 March 1940 at the AG Weser yard at Bremen, launched on 10 October and commissioned on 2 January 1941 under the command of Kapitänleutnant Richard Zapp as part of the 2nd U-boat Flotilla.
The Bay of Biscay is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Point Penmarc'h to the Spanish border, and the northern coast of Spain west to Cape Ortegal.
German submarine U-91 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II.
The first time the Allies knew about the "Thetis" was in a coded radio message to all U-boats transmitted on 11 January 1944. "Thetis" was introduced in January, when large numbers were released into the Bay of Biscay in July to simulate U-boat patrols during the Battle of Normandy.
Operation Overlord was the codename for the Battle of Normandy, the Allied operation that launched the successful invasion of German-occupied Western Europe during World War II. The operation was launched on 6 June 1944 with the Normandy landings. A 1,200-plane airborne assault preceded an amphibious assault involving more than 5,000 vessels. Nearly 160,000 troops crossed the English Channel on 6 June, and more than two million Allied troops were in France by the end of August.
