 GL Mk. III(B), with IFF | |
| Country of origin | UK |
|---|---|
| Introduced | late 1942 |
| No. built | 876 B's, 667 C's |
| Type | AA direction |
| Frequency | 2.750–2.855 GHz |
| PRF | 420 |
| Beamwidth | ~8 degrees |
| Range | 32,000 yards maximum, 27,000 yards against a light bomber |
| Precision | ±25 yards, ±1/6th degree at 32,000 yards |
| Other Names | Radar, Anti-Aircraft, No. 3 |
Radar, Gun Laying, Mark III, or GL Mk. III for short, was a radar system used by the British Army to directly guide, or lay, anti-aircraft artillery (AA). The GL Mk. III was not a single radar, but a family of related designs that saw constant improvement during and after World War II. These were renamed shortly after their introduction in late 1942, becoming the Radar, AA, No. 3, and often paired with an early warning radar, the AA No. 4, which was also produced in several models.
The Mk. III began development shortly after the introduction of the cavity magnetron in early 1940. The magnetron allowed radar systems to operate at microwave frequencies, which greatly reduced the size of their antennas and made them much more mobile and accurate. Having originally started work on the magnetron as part of the AI Mk. VIII air-to-air radar, the team was told to drop everything and develop a radar for AA use as quickly as possible. This turned into a fiasco; by the end of the year very little progress had been made and the team returned to working on airborne radars.
The magnetron has also been demonstrated to the Canadians and US as part of the Tizard Mission in the fall of 1940. Immediately following the visit, the National Research Council of Canada began development of a GL radar based on the UK design. The first examples of these GL Mk. III(C) (for Canadian) arrived in the UK in November 1942. British units of slightly more advanced design, GL Mk. III(B) (for British) arrived in December. 667 of the Canadian models were produced, with about 250 of these seeing service in the UK while most of the others were sent to the continent or remained in Canada. 876 of the British models were produced and saw more widespread service. Fifty Mk. IIIs were supplied to the Soviet Union.
Several improved versions of the Mk. III(B) were experimented with, but none were widely produced due to the 1944 introduction of the SCR-584 from the US, which provided both scanning and tracking in a single semi-trailer unit. Mk. III units found themselves relegated to secondary roles, as diverse as artillery spotting, coastal surveillance and weather balloon observation. Several upgrades were carried out for these roles, and modified weather units remained in use until about 1957/58. More radical development of the design also led to the greatly improved post-war AA No.3 Mk.7 radar, which served as the Army's primary AA radar until the removal of AA guns from service in the late 1950s.