Searchlight Control radar information

SLC

SLC Mark VI on a 150 cm searchlight being demonstrated for visiting MPs
Country of origin	UK
Introduced	early 1941 (early 1941)
Type	Searchlight direction
Frequency	204 MHz
Range	15,000 yards
Precision	~1° in bearing and elevation
Power	10 kW
Other Names	Radar, Anti-Aircraft No. 2, "Elsie", "Maggie", "Baby Maggie", SCR-768
Related	SCR-668

Searchlight Control, SLC for short but nicknamed "Elsie", was a British Army VHF-band radar system that provided aiming guidance to an attached searchlight. By combining a searchlight with a radar, the radar did not have to be particularly accurate, it only had to be good enough to get the searchlight beam on the target. Once the target was lit, normal optical instruments could be used to guide the associated anti-aircraft artillery. This allowed the radar to be much smaller, simpler and less expensive than a system with enough accuracy to directly aim the guns, like the large and complex GL Mk. II radar. In 1943 the system was officially designated Radar, AA, No. 2, although this name is rarely used.

The sight of searchlights swinging about wildly during the Blitz led a group of British Army engineers to begin development of SLC in early 1940. It was built using the electronics from the 1.5 m wavelength ASV Mark I connected to new antennas and a unique lobe switching system. The American SCR-268 and German Würzburg were generally similar in concept, but the SLC was small enough to be mounted directly to the light, as opposed to requiring a separate carriage. This greatly eased operation. There were several Marks of the system, differing in their mounting system, not the electronics.

The effect of using SLC was dramatic; aided by sound locators, in 1939 a searchlight had about a 1% chance of tracking a target, while with SLC this improved to 90%. SLC's greatest success was during Operation Steinbock in early 1944; SLC was involved in the vast majority of interceptions of German bombers, helping guide the night fighters without the need to use their own radars. They proved less useful against the V-1 flying bomb attacks later that year, but by this time improved radars like the SCR-584 were rendering the SLC concept obsolete. The US made a largely identical copy as the SCR-768 while an all-new design based on the same concepts was SCR-668.

SLC also proved useful to the enemy; in early 1942 an SLC and GL Mk. II were captured by Japanese forces at Singapore, along with the US SCR-268 in the Philippines.^[1] The SLC's Yagi antennas were unknown to the crews that discovered them, and they were surprised to find they were a Japanese invention. NEC produced a slightly modified version known as Ta-Chi 3, but it did not enter service.