One must always remember that Radar is line-of-sight and probably had a max range of 15Km for surface objects, whereas for air objects it is the limit of it's detectors.
There is a note somewhere that on a good day a UBoat hydrophone operator could hear a single ship at a range of ~15km, but a whole convoy anywhere between 50-100Km.
Radar definitely helps in poor visibility weather, and spotting a/c, but for surface objects I'd rely more on hydrophone.
Before anyone goes into a spin - I speak from experience (qualified military Radar Engineer (airborne/navy) , plus other airborne and navy systems ). Now I'm just generally
overqualified for what I do....
A little edit:
"Radar is line-of-sight" => that is for the high frequency stuff (small aerials) carried on the subs.
"Over the Horizon" stuff is for aerials bigger than a sub itself.
