CHL was RAF operated while the CD sets were British Army. It's the usual inter service rivalry. CD sets were developed from the Army's GL (Gun laying) radar sets for directing coast defense batteries rather than general search sets. They could function as the later however. So, CD was usually found near coast defense sites. CHL was developed from the same basic technology to fill gaps in CH's coverage, particularly at low altitudes. Organizationally, CHL tied into the air defense system while CD operated locally with Royal Artillery coast defense guns. In addition, the Army had mobile RDF radars as well as the mobile GL sets. The main point is that Britain had considerable numbers of radar sets in service in 1940 that could have and would have discovered a German invasion fleet well before it arrived. It's interesting to note that many of the British sets were really pretty crude constructions. CHL and CD radars were usually mounted on wooden platforms using a wood and chicken wire antenna with simple dipoles. They lacked automatic switching to allow the antenna to be both a receiver and transmitter and instead used separate portions for that purpose, of like CH used entirely separate antennas. CHL was rotated using bicycle chain and sprockets, and in early versions rotated by hand.