Both the US Army and Navy considered the idea too complicated and work ended in 1939. O’Brien's friend, Harvey F. Schwarz, was chief engineer of the Decca Record company in England. In 1939 O’Brien sent him details of the system so it could be put forward to the British military. Initially Robert Watson-Watt reviewed the system but he did not follow it up, deeming it too easily jammed (and likely due to the existing work on the Gee system, being carried out by Watt's group). However, in October 1941 the British Admiralty Signal Establishment (ASE) became interested in the system, which was then classified as "Admiralty Outfit QM". O’Brien brought the Californian equipment to the UK and conducted the first marine trials between Anglesey and the Isle of Man, at frequencies of 305/610 kHz, on 16 September 1942. Further trials were conducted in the northern Irish Sea in April 1943 at 70/130 kHz. It was decided that the original frequencies were not ideal, and a new system using a 14 kHz inter-signal spacing was selected. This led to the common 5, 6, 8 and 9"f" frequencies, used throughout the life of the Decca system. 7"f" was reserved for a Loran-C-like extension, but never developed. A follow-up test was carried out in the Irish Sea in January 1944 to test a wide variety of upgrades and production equipment. By this time the competing Gee system was known to the Admiralty and the two systems were tested head-to-head under the code names QM and QH. QM was found to have better sea-level range and accuracy, which led to its adoption. A three-station trial was held in conjunction with a large-scale assault and landing exercise in the Moray Firth in February/March 1944. The success of the trials and the relative ease of use and accuracy of the system resulted in Decca receiving an order for 27 "Admiralty Outfit QM" receivers. The receiver consisted of an electronics unit with two dials and was known to its operators as the "Blue Gasmeter Job". A Decca chain was set up, consisting of a master station at Chichester and slaves at Swanage and Beachy Head. A fourth decoy transmitter was located in the Thames Estuary as part of the deception that the invasion would be focussed on the Calais area.  21 minesweepers and other vessels were fitted with "Admiralty Outfit QM" and, on 5 June 1944, 17 of these ships used it to accurately navigate across the English Channel and to sweep the minefields in the planned areas.