Most radars used by the British during WWII were ground-based radars; this meant that preventing the Germans from capturing them was as simple as preventing the Germans from moving through to the rear areas where they were stationed (or from crossing the Channel). When such an advance was threatened, then parties were detailed to destroy the radar systems. The main time where this happened was during the Battle for France in 1940, as the rapid German advance caused disarray in Allied lines. As the British withdrew from France, radars were evacuated where possible, and destroyed if escape was impossible. When the steamer Crested Eagle, carrying an Army gun-laying radar, ran aground near Dunkirk, a naval demolition party was put aboard to destroy it before the ship could be captured. Despite these precautions, a radar was captured near Boulogne. Fortunately, it was one of the more primitive mobile sets, giving the Germans little idea of the capabilities of British radar.

Initially, airborne radars (and other secret electronic equipment, like receivers for the Gee radio-navigation system) were equipped with demolition charges that would destroy the equipment in the event of a crash or shoot-down. The aircraft's crew were to set the detonator as they left the aircraft. It would then, after a short delay, set off the charges and destroy the radar. It was a generally reliable system, but could fail if the aircraft ditched at sea. However, once the radars began to introduce the cavity magnetron, this system was no longer really usable. The magnetron was a large block of copper, with a series of intricate cavities carved into it which made it useful as a radar component. A series of experiments were carried out at Farnborough to work out the best way to destroy it. The first option tried was simply the old method, but with a larger two-ounce charge. During a test, it blew a ten-foot hole in the fuselage of the aircraft and reduced the magnetron to fragments. Unfortunately, the workings of the magnetron could still be determined from the shrapnel. Another method tried was to use one charge to blow the magnetron out of the aircraft before using a second larger charge to destroy it. This was rejected as the explosion of the first charge was powerful enough that it could blow the aircraft apart in flight. The use of acids was also considered, but this was thought to be impractical. As such, there was no way to destroy radars using the cavity magnetron. This was not a problem at first; the first radars using it were air-intercept radars, used by night-fighters operating over the UK. If one of these aircraft was shot down or crashed, then the wreckage would end up on friendly territory, with no chance of it falling into German hands. Radars using magnetrons had also been developed for maritime patrol aircraft, where it was felt there was little chance of their wreckage falling into German hands. However, in the latter half of 1942, the magnetron was used to create the H2S ground-mapping radar. This was designed for use by RAF Bomber Command, to aid with navigation in night-bombing raids over Germany. In this role, it was almost certain that wreckage containing a magnetron would fall into German hands. Even so, it was felt that H2S enhanced Bomber Command's abilities enough that this was a risk worth taking, and so H2S was put into the skies over Germany on the 30th January 1943. Just three days later, during the second attack using it, a Shorts Stirling carrying the radar was shot down near Rotterdam. The Germans were able to salvage it, though the salvaged parts were destroyed in a bombing raid on Berlin just a month later. Even so, the Germans were able to find replacements quickly.