The capitulation of Singapore has been laid on the commander, Arthur Percival. The actual reasons are many, muddled chain of command, japanese air superiority and years of neglegted ground forces just to name few.
But what if Percival actually had been more gifted commander:
Japanese forces invade Malay in December 1941, Commander of the Commonwealth Forces realizses after few clashes that Malay cannot be held and orders evacuation of air and ground forces south to Singapore while mounting delaying operation with rear guard.
By the beginning of January Japanese reach Johore strait and prepare to take Singapore. Commkonwealth units, while shaken and harassed from the air are still coherent fighting force. Meanwhile their leader has gathered uppred echelon for final conference before pending invasion. Feathers are smoothed (or roughed if needed), but in the end the Dutch, New Zealand and British forces are gathered under unified command.
25. January Japanese assault Sarimbun Beach, after 20 hours of intensive fighting and commitment of 2 brigades from the 11. Division the assault is repulsed. While artillery and air bombardmend continue, Singapore still stands.
Now what happens? As long as ammunition holds Singapore stands a good chance of fighting of another assault. British pre-war planning calls for a naval task force to relief, but are hardly in a position to send one. Singapore would have tremendous prestige, Japanese are not able to just seal it and leave it sitting nor is Churchill just going to abandon it.
How would the Pacific War proceed if Singapore would have held?