 Most of 1938 was taken up with practical problems and development of ASV . One change was the use of the new Western Electric <unk> tubes in place of the earlier <unk> . These allowed a further increase in power to pulses around 2 kW , which provided detection of ships at 12 to 15 miles ( 19 – 24 km ) . Their test target was the Cork Lightship , a small boat anchored about 4 miles ( 6 @.@ 4 km ) from the White Tower . This performance against such a small vessel was enough to prompt the Army to begin work on what would become the Coast Defence ( CD ) radars . The Army cell had first been set up on 16 October 1936 to develop the Gun Laying radar systems . 
