The FuG 227 Flensburg was a German passive radar receiver developed by Siemens AG

Siemens AG

Siemens AG is a German multinational conglomerate company headquartered in Munich, Germany. It is the largest Europe-based electronics and electrical engineering company....

 and introduced into service in Spring 1944. It used wing-mounted dipole antenna

Dipole antenna

A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other , with a small space between them. The radio frequency voltage is applied to the antenna at...

e and was sensitive to frequencies of 170-220 MHz. It allowed Luftwaffe

Luftwaffe

Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....

 nightfighters to home in on the Monica tail warning radar

Monica tail warning radar

Monica was a range-only tail warning radar for bombers, introduced by the RAF in the spring of 1942. Officially known as ARI 5664, it operated at frequencies of around 300 MHz...

 fitted to RAF

Royal Air Force

The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

 bombers.

On the morning of 1944-07-13, a Junkers Ju 88G-1

Junkers Ju 88

The Junkers Ju 88 was a World War II German Luftwaffe twin-engine, multi-role aircraft. Designed by Hugo Junkers' company through the services of two American aviation engineers in the mid-1930s, it suffered from a number of technical problems during the later stages of its development and early...

 nightfighter equipped with Flensburg mistakenly landed at RAF Woodbridge

RAF Woodbridge

Royal Air Force Station Woodbridge, more commonly referred to as RAF Woodbridge, is a former Royal Air Force military airbase situated to the east of Woodbridge in the county of Suffolk, England...

. After examining the Flensburg, the RAF ordered Monica to be withdrawn from all RAF Bomber Command

RAF Bomber Command

RAF Bomber Command controlled the RAF's bomber forces from 1936 to 1968. During World War II the command destroyed a significant proportion of Nazi Germany's industries and many German cities, and in the 1960s stood at the peak of its postwar military power with the V bombers and a supplemental...

 aircraft.

Subsequently, further variants of Flensburg (Flensburg II to Flensburg VI) were developed for detecting Allied radar jammers. Only Flensburg II and III were used operationally.