This set of three images shows the three types of antennas used on the SCR-540 radar set as installed on an A-20, the P-70 prototype. This was the US copy of the UK's AI Mk. IV radar, the first airborne radar system for fighters, and the second airborne radar to enter service. It is predated only by months by the ASV Mk. I, developed using the same electronics as this set. There is a possibility that this is in fact a "real" AI Mk. IV, and not the -540, as one example is described by Bowen on page 179 of Radar Days as being fit to an A-20 for testing.