Which historical ship would be changed most by receiving one modern OTO Melara 76 mm gun?
Short answerHMS Repulse, because effective modern air defense might let both Repulse and Prince of Wales survive as Force Z.
NotesA single OTO Melara 76 mm gun would transform HMS Repulse most. Her machinery could supply the weapon, and its radar-directed rapid fire would make the Japanese torpedo attack in the South China Sea far more difficult. If Repulse survives and helps Prince of Wales survive, Force Z remains available during the opening Japanese advance. That result changes more than saving one frigate in a later war because two capital ships could affect the wider Malayan campaign. The counterfactual places a compact defensive system at a point of considerable operational leverage.