Mk.1a Window Launching Machine

Window Launching Machine Mk.1a prototype. The machine consists of an aluminium alloy box, containing three levels of trays for packets of Window radar counter measure foil. The trays are actuated by a system of chain drives and belts, which feed the individual packets to a chute at the rear of the machine. The chute dispenses the packets through a hole especially cut in the bomb bay doors of a bomber aircraft. A Motor and Winding Unit is also located at the rear of the machine. At the top of the machine are two suspension points to which can be fitted a pair of 1000 pound (454 kilo) Universal Bomb Carriers. The rear Carrier on the machine is modified, with the front and rear sections shortened. The machine is controlled by the navigator, using a Switch Box fitted with a control switch and indicator light that illuminates as each bundle of Window is released.

The Window Launching Machine Mk.1a was a device designed to dispense packets of Window radar counter measure foil. It was designed and developed by personnel of 199 Squadron RAF under the guidance of 424778 Flight Lieutenant Charles Joseph Merryfull RAAF in 1945. The squadron was part of 100 Group RAF whose task was to support operations by Bomber Command and other Allied forces by jamming German radar equipment and carrying out other types of electronic warfare. The machine allowed packets of Window foil to be dispensed from the aircraft at a chosen speed. A formation of aircraft fitted with the machine could release a carefully controlled pattern of Window, efficiently jamming the German radar. After the development of the machine by 199 Squadron it was generally adopted for use by 100 Group and fitted to their Stirling and Halifax aircraft for operational use. Merryfull’s expertise with Window was recognised, and he was allowed to establish a research and development station at Swanton Morley. After the completion of the first working version of the launcher, Flt Lt Merryfull continued work on the modification of the equipment for installation in Mosquito aircraft. While undertaking a test flight on 8 July 1945 to carry out trials with new Window dispensing tanks, the port tank failed and (probably) struck the tailplane. The pilots recovery of the aircraft caused the starboard wing to fail & the Mosquito broke up in the air. Sq/Ldr Charles Merryfull was posthumously awarded the MBE for the development of the foil automatic dispersal of window strips.