the RAF was able to seriously disrupt German night fighter operations by attacking them directly. Aircraft that did survive reported that there was no warning of the attack, and it was quickly surmised that the RAF had introduced a new microwave AI radar. This led to the rapid introduction of the Naxos ZR, tuned to the Mk. VIII's frequency and equipped with rearward facing antennas. Altogether, about 700 Naxos Z and ZR's were produced. Submarine use Given the concerns over the possibility of losing a magnetron to the Germans, for some time through the summer of 1942 the RAF limited future deliveries to Coastal Command aircraft for anti-submarine duties, where the possibility of capture was remote. However, Bomber Command fought this decision and by the time deliveries started late in the year they received all of the units. This was reconsidered once again when it was becoming clear the U-boats had been equipped with some sort of detector for the existing ASV Mk. II radar, as they could be seen disappearing on the radar as the aircraft approached, and this was put to fearsome use in early 1943. A new agreement was reached where Coastal and Bomber Command would split the deliveries about 65/35. When the first of these ASV Mk. III radar systems began reaching service in early 1943, the effects were profound. Once again British aircraft could attack submarines with no warning until the last seconds when the Leigh light was illuminated, far too late for the submarine to take defensive action. A new phase started where British aircraft pressed into the Bay of Biscay and German submarines were told to remain on the surface and fight it out in daylight rather than risk almost certain death at night. This led to a crash program to equip their fleet with a variation of Naxos that could detect the new radar. The resulting Naxos U initially proved to have very short detection range, too short to be really useful. This led to a series of new antenna designs before the final Fliege (fly) semi-parabolic system was introduced. This had the distinct disadvantage that it was not waterproof and had to be removed from its mounting and taken inside in order to dive. Even with this antenna, warning times were on the order of one minute. An even later version, Naxos ZM, spun the antenna at 1,300 RPM to display