The IFF system broadcast a short pulse of radio signal whenever it heard the pulse from one of the ASV radars, and its signal was so powerful that the crews could pick it up at from base, making the return flight to RAF Leuchars much less eventful. The crews took to naming the beacon "Mother". In February 1940 a collection of early combat reports was compiled in order to better understand how to improve the system. By this time the Mk. I had also been installed on Blackburn Botha and Bristol Beaufort aircraft. The reports noted that the system was useful for detecting ships at night or in bad weather, but suffered from the fact that enemy shipping typically hugged the coastline where the returns from the land often swamped the ship's returns. It was also useful for guiding an attack when the cloud cover was below , as they could press an attack without ever being seen. Based on the experiences of the Mk. I units in the field, in January 1940 Gerald Touch began designing a new set while working at the RAE. Hanbury Brown joined him in February 1940. The new ASV Mk. II design was essentially a rationalized and cleaned up Mk. I, differing little in terms of the electronics, but considerably in terms of layout, wiring and construction. Among the changes was the separation of the receiver electronics from the display so either could be fixed by swapping them out separately, and using a selection of standard electrical connectors on all of the cables. As a result, Mk. II was far more reliable than Mk. I; it did not offer increased performance, but maintained that performance in spite of rough service and was much easier to fix in the field. The only other major change was to move the operational frequency from 214 MHz to 176 MHz because it was found the Mk. Is were interfering with naval radio beacons. An order for 4.000 units was placed with EKCO and Pye. For reasons unknown, the contract negotiations required considerable time to finalize, and throughout the production run it battled for precedence with the AI units and Chain Home Low which also made use of the Pye strip. The first Mk. II units began to arrive in the summer of 1940, and by October 1940, 140 transmitters, 45 receivers and 80 displays had been delivered. By the end of March 1941 that had increased to 2,000 transmitters and 1,000 receivers. II scored its first success on 30 November 1940 when a Whitley Mk. VI damaged U-71 in the Bay of Biscay.