The Radar equipped B24’s helped a little bit.
“The Radar equipped B24’s helped a little bit.”
By the time Allied war planners noticed that Imperial Japan’s war effort was critically dependent on merchant vessel traffic (from China/Korea, mainland Asia, East Indies etc; and in Home Island coastal waters), USN’s submarine force had already caused a major impact, and by war’s end accounted for the great majority of Japanese merchant ships destroyed.
But anti-ship campaigns conducted by air took their toll.
Night attacks by USAAF bombers (many by B-24s, as noted) and USN patrol aircraft (many by PBY “Black Cat” units) were by far the most daring, and likely the most unnerving, from an aircrew standpoint. But most of these attacks were carried out far away from Home Island waters, simply because no Allied aircraft had the range to carry the fight to the enemy’s front yard.
Quite late in the war, it was decided that USAAF’s B-29s (the sole Allied aircraft with the range and payload to get the job done) would haul naval mines from the Marianas to lay minefields in Home Island waters, to interdict local merchant vessel traffic.
In terms of effort applied versus result, this final campaign was the most effective, cutting total transported tonnage by some 90 percent, eventually accounting for some eight percent of the Japanese merchant vessel tonnage lost.
See the US Strategic Bombing Survey for additional results.