"SG" Microwave Surface and Low Air Search Radar
    The SG radar, along with the TBS radio, was certainly the equipment that prevented the U.S. Navy from being swept aside during the fierce night battles fought in the dark waters of the Solomons Islands chain.   

    The SG radar was state of art technology when introduced in 1942. It had long been clear that the shorter wavelength would make for a more efficent radar at least on low altitude, but there had been no energy source powerful enough to create such frequencies. The British had, however, achieved that goal and when in 1940, British and American scientific advantages were exchanged, the British handed the Americans the magnetron, capable of managing just those requirements needed for microwave radar.   
In just six months, a first prototype radar was build, becoming the forerunner of all microwave (S-band) radars: SE, SF, SG, SH, SJ. Of these, SG and SJ were the most important.   

    Microwave frequencies made for smaller antennas while retaining good performance. The SG proved this.   
It was the first such radar to incorporate the Plan Position Indicator (PPI), the display commonly associated with radar today, in which a number of circles set at certain ranges with the radar-carrying ship in the center gave the radar observer a clear view of the area around him. Navigation, position-holding, threat evaluation all became much easier with a PPI.   

    The SG radars small size made it possible to fit it to most U.S. warships. It was first tried on the destroyer Semmes in June 1941, and starting April 1942, it was placed on virtually all U.S. warships as large as a destroyer. Over 1000 total were build of all versions, but only SG to SG-3 were build during the war. SG, SG-1, SG-2, SGb and SG-1b were the most frequent and earliest variants, 955 of them being build up to 1943, and varied only slightly from each other, mainly being field modifications of the earlier sets. SG-3 incorporated a new antenna and used a shorter wavelength of 8.6cm, giving better range and resolution and a more precisely defined beam. It was only produced starting mid-1945 and did not come into use during World War II.  

A SG radar of the original type being tested. 
There were seven modifications of the design, some with different antennas. 
Stats SG
Peak Power: 50 kW  
Pulse Repetition Frequency: 775  
Accuracy: 200 yds, 2°  
Resolution: 400 yds, 2-3°  
Weight: 3000 lbs  
Ranges: Battleship 22nm, destroyer 15nm, bomber at 500ft 15nm