This mobile searchlight was presented in the Illustrated London News under the headline “Sky-Grids to Locate Air raiders: Britain’s Most Ingenious Searchlight.” And ingenious it was. Its inventor, seen in the lower picture, was Major Jack Savage. Already famous in 1931 for sky-writing with coloured smoke, Savage had created this unique anti-aircraft searchlight, said to be the most powerful in the world, to throw its beam in the form of a hollow grid that enabled the height, speed and direction of enemy aircraft to be speedily plotted. The article appeared in December 1931, at which time the invention had already been tested by the War Office. It was capable of emitting 3,000 million candlepower. The secret of this remarkable equipment was that the beam, which could create many different patterns, consisted of 300 parallel beams, each deflected by a mirror along the path required.
The lorry on which the searchlight was mounted, and which generated the electric current, was a Tilling-Stevens – also a fascinating piece of machinery. These commercial vehicles carried the proud designation “Petrol-Electric” on a casting below the radiator. They were true hybrids, although with no battery accumulation or modern electronic control, they were inefficient.
The W.A. Stevens company was established in Maidstone in 1897 by William Arthur Stevens. It made its first petrol-electric vehicle using the patented designs of Percival Frost-Smith. A petrol engine was connected to an electrical generator and the current produced passed to a traction motor which drove the rear wheels. Frost-Smith was Managing Director of Tilling-Stevens Ltd in 1915/1916.
These vehicles were popular with transport undertakings in the UK and abroad, being simpler to operate than conventional lorries and buses with non-synchromesh crash gearboxes. World War I forced Tilling-Stevens to focus upon bus operators, since the Army considered their petrol-electric chassis unsuitable for use in France. The low-mounted electrical items were considered too vulnerable.
Because many men were trained during the war on vehicles with conventional gearboxes, and as gearbox development made those vehicles quieter, more reliable and lighter, and thus more economical to run, the popularity of the Tilling-Stevens system declined after the Great War. By the mid-1930s, the company was producing chassis with petrol and diesel power and conventional transmissions.
However, Tilling-Stevens did take advantage of the electric transmission to move into specialised markets where the transmission could be used as a generator. Early turntable ladder fire engines used the system for lighting arc lamps and for raising the ladders. And, of course, the system was ideal for use with the Savage Searchlight Projector that features in this week’s Snapshot.
Picture courtesy of the Richard Roberts Archive