Some of the islands the Japanese were on they went into their caves and the battleships fired a lot of 16 inch shells and yet when the smoke cleared they crawled out and shot the guys coming ashore
Bunker Busters are what they need then and now drop a string of bunker busters from a B-52 and set timers for them all to go off at the same time collapse the tunnels and bury them in one pass.
Bring back flame throwers