NEW AIR BARRAGE

Evening Star, Issue 23693, 28 September 1940, Page 7

NEW AIR BARRAGE

IMPROVED ANTI-AIRCRAFT METHODS CONCENTRATION OF FIRE Recently the German raiders over London encountered the most terrific anti-aircraft barrage in the history of aerial warfare. The tactics of the previous four nights were changed. The searchlights were switched off and the ground guns came increasingly into play (writes the military correspondent of the ‘ Sydney Morning Herald ’). Military authorities admit that the new barrage is based on new methods of electric prediction. This should enable a local concentration of fire in the path to be taken by enemy warplanes. It is also reported that bigger guns are being used. This probably means that production 'of the newer 4.Sin anti-aircraft gun is now so great that the older 3.7 in may be replaced in most units. There is also a new Bofors gun, much bigger than the little I.7in which British has been manufacturing under Swedish license in the last three years. The trouble with the Bofors was that, although its sighting apparatus and its super-sensitive shells were very good, it was not effective beyond a height of 10,000 ft. The 3.7 in gun, on the contrary, was useful up to almost 30,000 ft, and the 4.5 in to over 40.000 ft.

It is fair to say, however, that the main use of the 3.7iu is for planes flying in the belt just above 20,000 ft, and the 4.5 in for those at about 30,000 ft, These heights constitute the maximum effective ceiling under service conditions. The shells from each of these two types of gun burst over a circle roughly 100yds in diameter; and it is clear that, if some predictor enables a more accurate and more rapid calculation of tho angle! of fire, a heavy local barrage is possible in front of a plane. •On the other hand, the difficulties of hitting a target moving at between 200 and 300 miles an hour and constantly changing course and height are obvious. The Vickers and Sperry predictors, which were fitted to anti-aircraft guns last year, are extremely accurate if the operator has a few- seconds to focus, and if the plane keeps its course ,for a further few seconds and if the rangefinder has calculated distance correctly. If better predictors allow improved accuracy up to a higher ceiling, tho whole problem of the bomber will bo changed, for certain types of bombers will not be able to fly sufficiently high, with full cargoes of bombs, to escape accurate ground fire, while others will be forced so high that any accuracy of bombing will be out of the question.