Undoubtedly ... either stick with the ARCADIA decision,
For a 1943 invasion of continental Europe to happen, it will need three things - an early decision, ships and more ships. Therefore, the Allies need to decide what they arent doing, in order to free those ships. The Pacific counter-offensives being abandoned clearly saves shipping - a defensive line of India -> Australia -> New Caledonia -> Midway -> Hawai'i would possibly do it (note the US public, and Congress, expect attacks on the Japanese). This will also free US marine divisions for spearheading any invasion. Moving much to most of the Bomber force from strategic bombing onto convoy protection will also save ships, but this will presumably be resisted by the Air Forces concerned. A big call is declining to reinforce the 8th Army between the First and Second battle of El Alamein - if they are reinforced, then that isnt exactly ignoring North Africa.
Undoubtedly ... either stick with the ARCADIA decision that an invasion goes forward in 1943, or - at the latest - make a firm decision at the 2nd Washington conference, which given the results of Midway, is actually in the realm of the possible.
The obvious (albeit different than the OP) path forward is to cancel WATCHTOWER-CARTHWHEEL and use the resources freed up (shipping, largely, but also naval forces) to enlarge TORCH from five division equivalents (four infantry and one armored) to six division equivalents (five infantry and one armored); using the entire British 78th Division as that "fifth" infantry division as a floating reserve allows a second-phase landing farther east in North Africa (Tunis or Bizerte) which, if Esteva actually will fight, gives the Allies Tunisia by the New Year, 1942.
Putting the US 1st Division and 1st Armored Division (-) ashore as the "Eastern Task Force" at Phillipeville and/or Bone (Skikda/Anaba, today) and the reinforced 34th Division as the "Center Task Force" at Algeirs, while simply screening Oran with naval forces (
Wasp, Indiana, and escorts, for example, since they're not in the South Pacific) makes an early end to the Tunisia campaign that much more likely.
A US corps built aroiund the 1st Armored and 1st Infantry divisions, with the 9th Infantry coming up, under (presumably) Patton meets 8th Army under Montgomery at Tripoli sometime early in the winter of 1943.
Note this leaves Anderson, Allfrey, Crocker, a British army headquarters, two British corps headquarters (V and IX), 6th Armored Division, three infantry divisions (1st, 4th, and 46th), and two tank brigades (21st and 25th) that (historically) went to North Africa in 1942-43 in the UK for France.
As a side note, without Guadalcanal and the Solomons, no additional US divisions leave the West Coast for the Pacific after Midway; as it is, that gives Nimitz et al no less than the following - which were already in theater before June: 1st Marine Division, 2nd Marine Division, 24th, 25th, 27th, 32nd, 37th, 41st, and Americal, plus the Australian 6th and 7th (AIF) divisions, and the 3rd NZ division; in addtion, the Australian 1st Armored Division (AIF), and the useful elements of the AMF divisions (six infantry and two cavalry/motorized/armored at various times during 1942) plus the equivalent NZ forces at home. The only obvious reinforcement would be the US 3rd Marine Division, formed in 1942, which would round out the I MAC. Should be more than enough for a reinforced campaign in Papua/NE New Guinea in 1942 and garrisoning/training for a 1943 offensive into Micronesia.
Historically, in 1942-43 (before HUSKY), the Allied troopship pool (point to point and amphibious) accomplished the folllowing, using combat divisions as the basic metric:
a) From the US to the ETO: 1st, 2nd armored; 1st, 3rd, 5th, 9th, 29th, 34th, 36th, 45th, 82nd Airborne;
b) From the UK to the Med: British 6th Armored; British 1st Airborne; British 1st, 4th, 46th, 78th divisions; Canadian 1st Division;
c) From the Med to the Indian Ocean and Pacific (after June, 1942 and before July, 1943): British 6th Infantry Division (aka 70th Infantry Division); 5th Indian Division; Australian 9th Division;
d) From India to the Med (after June, 1942 and before July, 1943): British 5th Infantry Division;
e) From the US West Coast or Hawaii to Hawaii, Alaska, or the South Pacific (after June, 1942 and before July, 1943): 1st Marine Division; 2nd Marine Division; 3rd Marine Division; 7th Infantry Division, 25th Infantry Division; 33rd Infantry Division; 40th Infantry Division; 43rd Infantry Division.
Totals are 30 divisional-sized movements in the period 06/42 to 07/43; these include two trans-oceanic assault landings (US 3rd and 9th divisions in TORCH); in addition, of these 30 movements, at least a third were lengthier movements to the Pacific theater(s), which required time-spans significantly greater than an Atlantic crossing; it's a fair estimate to say that the 30 historical movements above would have (conservatively) been the equivalent of 40-45 trans-Atlantic movements.
And realize the above were not, by any stretch, a maximum effort; almost all of these were conducted using the Allies pool of point to point troopers, meaning pre-war passenger liners converted to troopers - and these were the exact same ships used to support the major Allied (especially US) movements to forward theaters in 1943-45. Very few dedicated troopers were built duing WW II; the vast majority of such ships were prewar passenger ships taken up from trade and converted to troopers. These varied from the "monsters" like
Queen Elizabeth and
Queen Mary (capable of carrying a division at a time) down to smaller shops (the US liners
Lurline and
Matsonia, for example) capable of carrying an RCT/brigade group equivalent.
The other point about trans-Atlantic troop lift is that while sending troops out to the Pacific or India essentially required converted liners, the trans-Atlantic lifts could be done in amphibious transports (US APA, British LSI),
and, if necessary, in landing ships (US-built LSTs, for example) or freighters (Libertys, etc). It would be rugged, but certainly not impossible.
So that would suggest that by the summer of 1943, the Allies could certainly have all the British and Commonwealth divisions that (historically) were available for OVERLORD and had been organized in 1942 (so 13, Guards and 11th armored; 3rd, 15th, 43rd, 49th, 52nd, 53rd, 59th infantry; Canadian 4th and 5th armored, 2nd and 3rd Infantry), plus six (1st Airborne, 6th Armored, 1st, 4th, and 46th infantry, Canadian 1st Infantry) that would have not been needed for North Africa or Sicily (19); plus as many as the pre-war US divisions that had not been sent west prior to July, 1942 in the ETO, meaning: 1st, 2nd, 3rd, 4th, 5th armored; 1st Cavalry; 1st, 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th, 26th, 28th, 29th, 30th, 31st, 33rd, 34th, 35th, 36th, 38th, 40th, 43rd, 44th, 45th, 82nd Airborne, to a potential total of 30 US, 14 British, and 5 Canadian, or 49 total.
The above does not, of course, include the British and Commonwealth divisions historically in North Africa at this point that served in the Med or NW Europe in 1943-45; these add the British 1st and 7th armoured; 50th, 51st, 56th, and 78th divisions; 4th, 8th, and 10th Indian divisions; 3rd and 5th Polish divisions (and presumably the 1st Armored, as well); and a South African division (1st Infantry or 6th Armored); 2nd New Zealand and 9th Australian are in the mix as well, for another 12-15.
At the same time, the British 2nd and 5th were already out east (India, Ceylon, or Madagascar), as were the Indian 7th, 14th, 17th, 19th, and 20th.
Then realize that the Allied forces embarked for HUSKY, afloat and combat loaded, amounted to eight Allied divisions (US 2nd Armored and 1st, 3rd, and 45th infantry, British 5th, 50th, and 51st infantry, and Canadian 1st Infantry, plus a separate infantry brigade and three separate armored brigades) and the realities of the Allied capabilities in the summer of 1943 become clear...
Especially when it is understood that in 1943, along with army groups in Tunisia, Sicily, and Italy (including an army group-sized assault for HUSKY and corps-sized landings for BAYTOWN and AVALANCHE), the Allies sustained corps-sized expeditionary forces in both the Southwest and South Pacific theaters, division-sized amphibious assaults in both those theaters as well as the North and Central Pacific, as well as air offensives the size of POINTBLANK and STRANGLE (much less those in the Pacific), and major trans-oceanic supply initiatives to aid the Soviets in three different theaters, and it
really becomes clear.
Best,