[doorgunner69]

Just think how easily a hostile submarine could sneak up on them if the combat center was not aware of even a huge merchant ship making all sorts of sonar racket and a RCS the size of a huge building.

The navy used to have a radar dedicated to surface search, the SAS-something IIRC. Dunno what they have now, that was 20 years ago.

Seems the SPS-73 is the current radar for navigation.:

"The AN/SPS-73(V)12 Radar Set is currently installed onboard approximately 100 ships across CVN, CG, DDG, LHA, LHD, LPD, LSD, LCC, PC and MCM ship classes. "

[PIF]

Great! But you have to turn it on first, or barring that actually look at it.