The game shows the radar set but they do nothing until the first SJ set come out in June 1942. If you start a career in mid 1942 your sub will have both SD and SJ but always check each time you are in port including when you first start your sub wont always have the best radars equiped.
In 1945 you can get SV which is supposed to be air search radar but in the game it does everything for some reason
though it was designed for air search not air and ground search if you look at photos of SV equiped subs you will see that have an SJ-1 dish as well of course the SV did not appear on any sub until Aug 45 so it is like the mk.16 a device in Sh4 that never saw actual combat in WWII. The SD wont show contatcs on your sets. It really should have its own A-scope but lacks one in the game the real thing simply let you know that something was in the sky within its range but gave no drectional data often the lookouts where as good or better at spotting planes as the SD was.I wish they where more accurate with the radars fro example the first SJ did not have PPI.