Here's a couple factors, one plus, one minus.
The minus is that sea state would have a deleterious effect on low
altitude pickup to the point where a good pair of binoculars would
have greater range. By low altitude here I mean sea-skimming to where
the jet exhaust is blowing up spray.
The plus effect is that a direct vision cathode ray tube (actual radar
blips on the scope) adds about 3 db to the radar's effectiveness
because the human eye/mind integrates the information and can discern
targets below the noise peaks - because noise is random and the radar
blis are not. It takes some experience but it definitely works.
So a 60's type radar would still be fairly effective aginst aircraft
out of the sea return, effective enough for fire control purposes.
Against the extremely low altitude target - when the CV Eisenhower was
working up the PRANG A7s could get at it by such an approach.
Walt BJ