Johnny, the advent to Radar provided a much improved (over the human eye) navigation and target detection tool even in the best weather. Visibility over the ocean can be problematic even under what are nominally considered to be good conditions. There is a frequent daytime natural phenomena known as maritime haze caused by evaporating water that severely limits visibility even from a/c at altitude. The ocean is a big place and while visibility may extend to 10's of km (miles), there may be scattered clouds and haze that prevents identifying high value targets. Remember an aircrew is looking for a target typically painted 'haze gray' which doesn't help. The ships more visible wake is often the first indication one gets of its presence. I have been on more maritime search missions than I can count and unless we were covering a shipping lane, it was never easy, even with radar. Without radar, these maritime patrol mission searches would have been virtually impossible. In the old days, before Radar, nearly an entire squadron was carried and deployed to perform a maritime search. As radar became more available, progressively fewer aircraft were required as radar performance improved.