Er... after 1943 they had plenty of aircraft support, landed tanks, and battleships. Don't forget the Navy often pounded an island for days with naval big guns and aircraft before sending the marines in.
a battle ship was barely able to hit another battle ship at 5 miles on the open seas where they could see it, no less take out a bunch of small targets, dug in, and hidden in thick forests.
there was a reason that they had to barrage for days before a landing and those same barrages did not continue once troops were on the ground.
More than 5 miles, but of course they would pull up relatively close. You also had cruisers and destroyers, plus constant air sorties from Navy and Marine aircraft, including during the actual invasion.