Monica Tail Warning Radar

Monica Tail Warning Radar
Technical Information
Purpose/Function	Detect enemy aircraft approaching friendly bomber
Type	Radar
Frequency	300 MHz
Usage
User(s)	Great Britain
Yearintroduced	1942
[Source]

The Monica Tail Warning Radar or ARI 5664 was a specialized radar that was mounted on British aircraft during World War II, notably, the Lancaster.

Description

Monica operated at a frequency of about 300 Megahertz and outwardly appeared as a small rod made into a bent 'T' shape placed under the rear gunner which then connected to a larger apparatus inside the aircraft. Its purpose was to warn the gunners on the aircraft of an incoming enemy night fighter when darkness prevented full visibility. To detect aircraft, Monica sent out a signal into the air. If the signal hit nothing, then no sound could be heard, if it came back, a beep sound was played over the intercom. The closer an aircraft came to the device, the faster the beeps would play. The type worked fairly well in the early years of its employment. However, it was a major issue for the rear gunner when flying a large formation because the radar would pick up many false alarms which allowed real threats to go otherwise unnoticed.

However, the biggest flaw of the design was the creation of the German Flensburg Radar Receiver, which was first placed on German night fighters in early 1944. What Flensburg did was home in on the signals put out by Monica and used them to alert German night fighters as to the exact location of the bomber fitted with Monica.

History

Monica was developed around 1942 and was implemented promptly. The main developer of the design was Ted Cooke-Yarborough, a leading figure in the development of radar. Initially, Monica started out as a device to be placed in British fighter aircraft which were commonly shot down while performing ground attack runs due to a loss of attention to enemy aircraft. Trials ended up proving the device useful, though it ended up not being placed on fighter aircraft. Instead, it was added to all new British bomber aircraft from 1942 onwards. Despite the fears of Monica being used as a way to track British aircraft, the Telecommunications Research Establishment (TRE) assumed that any German aircraft tracking a British aircraft with Monica would be within range to be detected by Monica anyway. 

In late 1944, British Air Officer Commanding-in-Chief of Bomber Command, Sir Arthur Harris ordered all Monica devices removed from British aircraft following the discovery of the Flensburg Radar Receiver. It is thought that Flensburg was first observed in a Junkers Ju 88G-1 which mistakenly landed at RAF Woodbridge. It should be noted that Monica was also sometimes used by the United States Army Air Corps.