This is a little more whimsical than usual for me, but it's an idea I've been kicking around for a couple of years now.
There are a couple of assumptions that we need in order to make this work.
1. At the suggestion of Roosevelt, who clearly sees war coming with Japan & doesn't want to have to change commanders in the middle of it, Adm. Hart (age 64, 44 years on active duty) is transferred to the Navy Dept. in Oct., placing RAdm. Glassford in command of the U.S. Asiatic Fleet, with a promotion to VAdm. (As part of the deal, Glassford gets a brief personal message from the Pres.)
2. VAdm. Glassford understands the reasons for his promotion just as clearly as Roosevelt does, so he immediately orders the Langley into Singapore. To be in compliance with the Washington Naval Treaty, the Langley had been converted from an aircraft carrier into an aircraft transport by having the forward third of her flight deck removed. On the eve of war, Glassford doesn't give 2 shits about the treaty & has it replaced-- a process we'll say takes 6 to 8 weeks.
3. Adm. Sir Tom Philips spends part of his cruise to the Pacific in late 1941 reading up on recent naval engagements, & the Battle of Taranto-- where British carrier aircraft decimated the Italian fleet-- makes a big impression on him. He therefore makes 2 key decisions. First, not to leave the carrier Hermes behind at Cape Town due to its slow speed, but to keep the Hermes with his squadron. And second, to confine his operations as far as possible to beyond the range of Jap land-based aircraft. (Of course it's impossible to stay out of bomber range, but he can keep to the outer limits of the range of enemy fighters, dive bombers, & torpedo bombers.)
Now, when Japan attacks on Dec. 7th (W of the International Date Line, on the 8th), the Allies have on-hand a task force consisting of the BB/HMS Prince of Wales, CB/HMS Repulse, CVL/HMS Hermes, CA/HMS Exeter, & 4 DDs. (Of course, due to having slowed down to accommodate the Hermes Philips doesn't quite get to Singapore before the 7th, so he's still in the IO when he gets news of the attack.) Another Brit task force is near at hand, consisting of the CLs/HMS Caledon, Danae, & Dragon, HMAS Hobart, & 2 DDs.
In addition, the US has the newly refurbished CVL Langley, the CA Houston, CLs Boise & Marblehead, the aircraft transport Wm. B. Preston, & at least 12 DDs.
On top of which, the Dutch bring 4 CLs, the DeRuyter, Java, Perth, & Tromp, & their 4 DDs.
The ABDA naval command also has over 40 subs & numerous freighters, tankers, tenders, maintenance & repair ships, & other fleet auxiliaries. Also, with Adm. Philips on-site, Adm. Hart gone, & therefore no friction between Hart & Glassford, there's no need to put Dutch Adm. Karel Doorman in command of ABDA naval forces. Philips will handle it, & now he's a lot more cautious about land-based air than he was in OTL.
Question : What could this reconfigured ABDA command have accomplished with 1 BB, 1 CB, 2 CVLs, 2 CAs, 10 CLs, 22 DDs, & over 40 subs, vs the overwhelming might of the IJN?
Predicting a win would be "out there", even for me. But Singapore fell on 15 Feb, Doorman lost the Battle of Java Sea on the 27th, Java was invaded on the 28th, & the ABDA forces surrendered on 9 Mar. How much better could they have done with a little careful husbanding of resources?
My own feeling is that 2 things would have been critical-- some kind of a surprize attack, employing the 2 CVLs. Tough to do at a speed of 16 knots for the Langley & 25 for the Hermes, but it might be possible to operate the Hermes as a forward attack base. The Langley is a couple hundred miles behind the Hermes & launches a strike that'll refuel from the Hermes before continuing to target. The Hermes launches its strike, then refuels & relaunches the Langley's strike, & then loiters to recover a/c from both strikes. The Hermes keeps all damaged a/c & sends the rest on to the Langley, then they both get the hell out of Dodge.
I've seen a 1930 photograph from before her conversion showing the Langley operating 24 a/c, so let's say that's her comfortable limit. Although during her last tour in the Far East the Hermes carried only 12 Fairey-Swordfish biplanes, her specs say she could operate up to 20, so let's give her 20. And planes are gonna be a serious problem, so let's get that out of the way right now. Glassford makes a personal appeal to the Pres. for some carrier planes & pilots to fly them, & Roosevelt sends him 50 of each-- 30 F4F Wildcats, 15 SBD Dauntlesses, & 15 TBD Devastators. This enables Glassford to earn a little good-will with the Brits by letting Philips get rid of those biplanes. The Langley operates 8 fighters, 8 dive bombers, & 8 torpedo bombers. The Hermes operates 6 fighters, 7 dive bombers, & 7 torpedo bombers.