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Early Centimetric Ground Radars - A Personal Reminiscence

Rowe describes the results of this programme. A dozen GCI sets had been installed by January, 1941, and with these and perhaps 100 AI sets, the casualty rate of enemy night bombers was raised from less than 0.5% to over 7%. In May, 1941, 102 bombers were shot down by night-fighters, and 172 assessed as probably destroyed or damaged*. These were prohibitive figures, and systematic enemy attacks by day or night virtually ceased.

It may be of interest here to note that the AI sets discussed above were Mks. III and IV. In a GEC Review paper(5) in 1993, Welsh describes the 'Foxhunter' radar, otherwise known as AI Mk. 24 (see fig. 1). In other words, British AI radar went through twenty variants in just over forty years. Even in 1993, one of the major problems is ground clutter: in the l940s, this was so severe that the early AI sets could see no target at a range greater than the night fighter's own height above the ground.

Obvious though it may have been to an objective observer that CH stations in general, and Ottercops Moss in particular, were largely redundant by 1943, it was not obvious to the station personnel and morale remained high. However, there was a steady drain of people, especially mechanics, away from the station so that by late in 1943 there was one fairly inexperienced mechanic and one fairly inexperienced technical officer left. As I explained to a senior Wing Technical Officer, this made a nonsense of the prescribed routine maintenance procedure: we were down to basic checks, as and when time permitted, to try to ensure the technical health of the equipment. By and large, the station was as fault-free under this austere regime as it had been under the daily attention laid down in the manuals, which required six or eight mechanics.

I was not sure how well this account had been received at Wing HQ, and it was therefore with some trepidation that I went to Wing to meet the same senior officer. He had news for me: I was to go on a centimetric radar course for three weeks at the end of the year. This would mean a second Christmas at Yatesbury, near Calne, in Wiltshire, a fact for which he apologized: No. 2 Radio School was not a welcoming place in winter. Thus began an involvement with centimetric techniques, and with centimetric radar in particular, that was to last for more than forty years.

The Advent of Centimetre Radar

In a previous papert(6), the present author called the magnetron "perhaps the most important scientific innovation of the second world war, even taking the atomic bomb into account". This view is borne out by Rowe**, who wrote that

"few in a position to judge would hesitate to name the cavity magnetron as having had a more decisive effect on the outcome of the war than any other single scientific device evolved during the war. It was of far more importance than the atomic bomb".

Rowe is careful to write of the cavity magnetron, invented in 1939, as distinct from simpler forms: the simplest of all, invented by Hull in the USA in 1921, was a diode with a cylindrical anode having a cathode along its axis, the current between the two being controlled by an axial magnetic field. Between 1921 and 1939, many variants and a voluminous literature had evolved: it is perhaps fair to say that no very consistent overall theory had emerged. However, there was a general tendency to use multi-segmented anodes. Hull's original magnetron had used only one anode: Habann (1924) had used two segments, and Postumus (1934) used four.

* These figures of enemy aircraft shot down, destroyed or damaged should be taken cautiously. For various reasons, some of them genuine (and not merely morale-raising propaganda), RAF claims of Luftwaffe losses in 1940 were nearly three times their post-war claims, and well over three times the losses listed in the German High Command diary.

** AP Rowe, as secretary to the Tizard committee, was one of only four men present at the Daventry experiment in February, 1935. In May, 1938, he succeeded Watson-Watt as Superintendent of the Bawdsey Research Station.


 

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