was a problem. This was solved by the second device, the WE-224 oscilloscope, recently acquired from Bell Labs. By feeding the signals from the two antennae into the X and Y channels of the oscilloscope, a single strike caused the appearance of a line on the display, indicating the direction of the strike. The scope's relatively "slow" phosphor only allowed the signal to be read long after the strike had occurred. Watt's new system was being used in 1926 and was the topic of an extensive paper by Watson-Watt and Herd. The Met and NPL radio teams were amalgamated in 1927 to form the Radio Research Station with Watson-Watt as director. Continuing research throughout, the teams had become interested in the causes of "static" radio signals and found that much could be explained by distant signals located over the horizon being reflected off the upper atmosphere. This was the first direct indication of the reality of the Heaviside layer, proposed earlier, but at this time largely dismissed by engineers. To determine the altitude of the layer, Watt, Appleton and others developed the 'squegger' to develop a 'time base' display, which would cause the oscilloscope's dot to move smoothly across the display at very high speed. By timing the squegger so that the dot arrived at the far end of the display at the same time as expected signals reflected off the Heaviside layer, the altitude of the layer could be determined. This time-base circuit was key to the development of radar. After a further reorganization in 1933, Watt became Superintendent of the Radio Department of NPL in Teddington. RADAR The air defence problem During the First World War, the Germans had used Zeppelins as long-range bombers over Britain and defences had struggled to counter the threat. Since that time, aircraft capabilities had improved considerably and the prospect of widespread aerial bombardment of civilian areas was causing the government anxiety. Heavy bombers were now able to approach at altitudes that anti-aircraft guns of the day were unable to reach. With enemy airfields across the English Channel potentially only 20 minutes' flying-time away, bombers would have dropped their bombs and be returning to base before any intercepting fighters could get to altitude. The only answer seemed to be to have standing patrols of fighters in the air, but with the limited cruising time of a fighter, this would require a huge air