 The problem was finding a radar that was suitably small ; CH radar 's huge towers obviously could not be swung about in this fashion . By this time the Army had made considerable progress on adapting the AI electronics to build a new radar for detecting ships in the English Channel , CD , with an antenna that was small enough to be swung in bearing . In 1938 , RAF pilots noted they could avoid detection by CH while flying at low altitudes , so in August 1939 , Watt ordered 24 @-@ CD sets under the name Chain Home Low ( CHL ) , using them to fill gaps in CH coverage . These systems were initially rotated by pedalling on a bicycle frame driving a gear set . A joke of the era " was that one could always identify one of the W.A.A.F. R.D.F. operators by her bulging calf muscles and unusually slim figure " . Motorized controls for CHL were introduced in April 1941 . 
