There are a number of interesting what ifs to consider.
Generally, scale back the size of the heavy bomber force and spend the resources on other things
Absolutely, at least for the RAF. Coastal Command was denied long-range bombers for far too long, and these aircraft were absolutely critical for winning the battle of the Atlantic.
Spend more resources in the Mediterranean front to push faster into Italy. Maybe even make an effort to retake Crete and Greece
Churchill was enamored with these ideas (US leaders deeply opposed to what was perceived as an attempt at protecting spheres of influence rather than winning the war), but I don't think more resources in the Mediterranean would have necessarily achieved much more. Italy is just terrible ground to fight over, with numerous mountain ranges that allow small defensive forces to delay an invader. Much of the most painful parts of the campaign (ex Salerno, Anzio) had to be conducted without the kind air superiority that would be present later in the war, since the Mediterranean theater is just a difficult place from an aviation standpoint: far enough to be difficult to maintain fighter coverage, near enough to be in easy bomber range, and not quite big enough for carrier groups at the time to fight effectively. There also were often simply not enough resources to pursue both a broader Mediterranean strategy and an invasion of western Europe.
Use the (reduced size) heavy bomber fleet for attacking targets close enough that they could be escorted by fighters. Say, any German military presence in Northern France; airfields, ports, transportation infrastructure like bridges or railway yards, fuel depots
While the large daylight attacks over Germany tend to overshadow everything else, plenty of 8th Air Force missions were over closer targets in France, as well all of the 9th "tactical" Air Force missions that were necessary to strike smaller tactical targets (airfields, RADAR stations, bridges, rail yards). In light of postwar surveys, using strategic bombers to strike small targets was a gamble, so it's not clear that much more would have been achieved. In addition, targets across all of France and the low countries needed to be struck to reduce German strength and reserves while also not disclosing the specific target of D-day.
All in all, if the Allies had played all their cards better, maybe they could have done D-day already late summer '43?
The US army really wanted to an invasion in 1943, and had to be restrained from it by practical constraints. Logistics of a massive assault on defended beaches with no hope of quickly capturing a usable port just weren't ready until 1944. Even with all the preparation, the Allied advance in summer/fall of 1944 was severely hamstrung by logistics.
Generally, scale back the size of the heavy bomber force and spend the resources on other things
Absolutely, at least for the RAF. Coastal Command was denied long-range bombers for far too long, and these aircraft were absolutely critical for winning the battle of the Atlantic.
Spend more resources in the Mediterranean front to push faster into Italy. Maybe even make an effort to retake Crete and Greece
Churchill was enamored with these ideas (US leaders deeply opposed to what was perceived as an attempt at protecting spheres of influence rather than winning the war), but I don't think more resources in the Mediterranean would have necessarily achieved much more. Italy is just terrible ground to fight over, with numerous mountain ranges that allow small defensive forces to delay an invader. Much of the most painful parts of the campaign (ex Salerno, Anzio) had to be conducted without the kind air superiority that would be present later in the war, since the Mediterranean theater is just a difficult place from an aviation standpoint: far enough to be difficult to maintain fighter coverage, near enough to be in easy bomber range, and not quite big enough for carrier groups at the time to fight effectively. There also were often simply not enough resources to pursue both a broader Mediterranean strategy and an invasion of western Europe.
Use the (reduced size) heavy bomber fleet for attacking targets close enough that they could be escorted by fighters. Say, any German military presence in Northern France; airfields, ports, transportation infrastructure like bridges or railway yards, fuel depots
While the large daylight attacks over Germany tend to overshadow everything else, plenty of 8th Air Force missions were over closer targets in France, as well all of the 9th "tactical" Air Force missions that were necessary to strike smaller tactical targets (airfields, RADAR stations, bridges, rail yards). In light of postwar surveys, using strategic bombers to strike small targets was a gamble, so it's not clear that much more would have been achieved. In addition, targets across all of France and the low countries needed to be struck to reduce German strength and reserves while also not disclosing the specific target of D-day.
All in all, if the Allies had played all their cards better, maybe they could have done D-day already late summer '43?
The US army really wanted to an invasion in 1943, and had to be restrained from it by practical constraints. Logistics of a massive assault on defended beaches with no hope of quickly capturing a usable port just weren't ready until 1944. Even with all the preparation, the Allied advance in summer/fall of 1944 was severely hamstrung by logistics.