▁ 1 9 4 2 ▁saw ▁the ▁fort ▁come ▁under ▁sust ained ▁fire ▁from ▁Japanese ▁ 1 5 0 mm ▁how itzer ▁batter ies ▁position ed ▁on ▁the ▁main land ▁near ▁T ern ate . ▁By ▁the ▁middle ▁of ▁March , ▁the ▁Japanese ▁had ▁moved ▁heavy ▁art illery ▁into ▁range , ▁opening ▁fire ▁with ▁ 2 4 0 mm ▁sie ge ▁how itz ers , ▁destroy ing ▁Fort ▁Dr um ' s ▁ 3 - inch ▁ant ia ircraft ▁battery , ▁dis abling ▁one ▁of ▁the ▁ 6 - inch ▁guns , ▁and ▁dam aging ▁one ▁of ▁the ▁arm ored ▁cas em ates . ▁Size able ▁port ions ▁of ▁the ▁Fort ' s ▁concrete ▁structure ▁were ▁ch ipped ▁away ▁by ▁the ▁shell ing . ▁The ▁arm ored ▁tur rets ▁were ▁not ▁dam aged ▁and ▁remained ▁in ▁service ▁throughout ▁the ▁bomb ard ment . ▁C ounter - b atter y ▁fire ▁from ▁Fort ▁Dr um ' s ▁ 1 4 - inch ▁guns ▁and ▁Fort ▁Frank ' s ▁ 1 2 - inch ▁mort ars ▁was ▁in effect ive . ▁With ▁the ▁collapse ▁of ▁American ▁and ▁Filip ino ▁resistance ▁in ▁B ata an ▁on ▁ 1 0 ▁April , ▁only ▁Fort ▁Dr um ▁and ▁the ▁other ▁har bor ▁for ts ▁remained ▁in ▁U . S . ▁hands . ▁ ▁On ▁the ▁night ▁of ▁ 5 ▁May , ▁the ▁ 1 4 - inch ▁batter ies ▁of ▁Fort ▁Dr um ▁opened ▁fire ▁on ▁the ▁second ▁wave ▁of ▁the ▁Japanese ▁forces ▁assault ing ▁Cor reg idor