What if HMS Indomitable had joined Force Z instead of one of its battleships?
Short answerIndomitable would probably let Force Z survive the initial Japanese air attack and give it reconnaissance and strike power, potentially disrupting the invasion of Malaya and producing a much stronger Allied fleet around Singapore.
NotesThe counterfactual swaps the ships' historical availability: Prince of Wales suffers the disabling accident while Indomitable reaches Force Z. Even a modest carrier fighter group would confront Japanese bombers operating unescorted near the limit of their range. Fighters, reconnaissance aircraft, and likely escorts would probably save the force from the historical attack. Survival then changes the defense of Malaya, Singapore, and the organization of ABDA Command.