spring of 1944, most of Bomber Command's aircraft carried it. Two hundred examples of the prototype model were produced before a slightly modified version was introduced, the Type 182A. This version had the range fixed at , with the side-effect that if the aircraft flew below this altitude the ground appeared as a ring of noise on the display. The Type 182 display was normally located at the radio operator's station, not the navigator's. This reduced the navigator's workload while also simplifying communications when a target was seen; the radio operator could easily communicate with the crew or send messages to other aircraft. Normally a number of blips would be seen, as other aircraft in the bomber stream made excellent returns. These remained largely stationary on the display as they were all flying roughly the same path, so enemy fighters were easy to see as dots moving around within the pattern of returns. If it was suspected a blip was approaching the bomber, they would change their heading and see if the blip followed; if it did, immediate defensive manoeuvring started. X band The resolution of any radar is a function of the wavelength used and the size of the antenna. In the case of H2S, the antenna size was a function of the bomber's turret opening, and when combined with the 10 cm wavelength, this led to a resolution of 8 degrees in arc. This was much coarser than desired, both for mapping purposes and for Coastal Command's desires to easily detect submarine conning towers. On 6 February 1943, work began on an X band version of the electronics, operating at 3 cm. This would improve resolution to 3 degrees when used with the same antenna. When priority was given to Bomber Command, Coastal Command responded by producing specifications for a far more advanced ASV system operating at 1.25 cm, but this was not completed by the end of the war. Work on 3 cm magnetrons had been ongoing for some time, and an AIS unit with such a device had been fitted to the nose of RAF Defford's Boeing 247-D, DZ203 as early as 1942. This aircraft had originally been supplied by the Canadian Defence Research Board to test US models of AI radar, and since then had been widely used in the development of several versions of AI, ASV and H2S. George Beeching had been assigned the