A few thoughts, I generally favor simple PODs in the not too distant past so this does not involve any changes in 1930s or the war up to that point. It is about making better use of available resources. Note, many of these are not my ideas, I am stealing them from others like Cryhavoc01 and we've hashed a number of these out on various threads and are generally things the British can begin putting in motion beginning in late 1940 after FIC is occupied in September. I am also keeping in mind force availability and the fact that Singapore is still at peace in 1940 and 1941 and therefore will not get the best stuff so there is a lot of make do with what you have in here:
Airpower - you need fighters, reconnaissance aircraft, and attack aircraft capable of sinking ships:
- Release four squadrons of Spitfires from the Home Islands for duty on Malta, permitting four Hurricane squadrons (No. 242, No. 249, No. 126, No. 185) for duty in Malaya. These are in addition to the five Brewster Buffalo squadrons sent to Malaya (No. 21, No. 243, No. 453, No. 67, No. 488/RNZAF).
- For a 10th fighter squadron, get the SAAF to cough of one of its P-36 squadrons (No. 3 or No. 4) for duty in Malaya.
- Instead of using the 50 Vought Vindicator dive bombers imported from the US as trainers, send them to Malaya to be land based dive bombers manned by FAA crews, this is enough for two squadrons plus spares.
- The Blackburn Skua was removed from the carriers in 1941, form two land based squadrons in Malaya as dive bomber squadrons, not fighter squadrons.
- There were still four operational Fairey Battle Squadrons into 1941 (No. 88, No. 98, No. 226, and No. 11/SAAF), the three RAF squadrons were all with Coastal Command serving in Ireland and Iceland, so stand up a couple of Battle Squadrons in Malaya for maritime patrol and anti-shipping missions.
- You still have your four Blenheim squadrons and two Hudson squadrons plus your small number of PBYs.
- The two Vickers Vildebeest squadrons (No. 36 and No. 100) are used as source of trained crews to round out the new squadrons standing up.
- Send the Vickers Wellesley equipped No. 47 Squadron from East Africa to Malaya for long range maritime patrol (a job it did in the Mediterranean for a good chunk of 1942).
- Logistics, logistics, logistics, an effort needs to be made throughout 1941 to acquire spare parts, tools, and other necessary components for keeping an air force in fighting shape.
- Get an experienced and qualified commander, my vote is Air Vice Marshal Quinton Brand, a South African who commanded No. 10 Group in the Battle of Britain and was a disciple of Dowding and Park, his main task of course will be to organize an air defense system for the peninsula.
Ground Forces - you need some better troops and armor, I appreciate other suggestions as well:
- Pull the British, Canadian, and Indian troops in Hong Kong out of that colony and send them to Malaya, this is a no brainer.
- As others have suggested, send whatever second or third rate tanks you can scrape up to Malaya to form an armored brigade (or two).
- Get a commander who will make do with what he has, train the snot out of his troops, and not give a lick about hurting the feelings of pompous colonial officials, yeah probably Montgomery here.
- Build fortifications on the island, you just might have to retreat to there.
- Other than the units on Hong Kong, I'm not sure what other ground forces might be available to send to Singapore at this time, maybe the third brigade of the 8th Australian Division?
I'll get you some other things and naval stuff in another post, I have to divert to making dinner now. Again, none of these things by themselves are war winners and some of what I am suggesting involves aircraft that are not world beaters by any stretch but are a damn sight better than what they had OTL and certainly a damn sight better than nothing.