If the Second World War had started in 1944 and not in 1939, it would have meant a very different naval situation, because the fleets of all the major navies would have been very different. We can thus base our wild guess on several pre-war plans and hypothetical scenarios of what naval forces might have looked like.
The ambitious “New Standard Fleet” called for 20 capital ships, 15 carriers, 100 cruisers, 186 ships forming 22 destroyer flotillas, and 82 submarines. This was a 10-year plan, running from 1936 to 1945, and in theory, was expected to see the arrival of 12 new capital ships on the Royal Navy list: five King George V-class, six Lion-class, and the Vanguard. The fleet would also be increased by the addition of existing ships such as the Hood, Nelsons, Renown, and Queen Elizabeths.
That is, by 1948, Germany had an infamous ‘Z’-Plan which is bound to be at an advantaged level of construction in case of war from 1944. For that, it would still have a plan for 10 battleships, 13 capital ships, four aircraft carriers, and a good deal of cruisers, destroyers, and submarines. However, it is most likely that by then, Germany would have got to complete only four ‘H’ class battleships and maybe two of its three planned battlecruisers to add to the Bismarck, Tirpitz, Scharnhorst and Gneisenau.
These naval ambitions were to have included seven new capital ships, eight large aircraft carriers, and 23 light carriers among others. By 1944 Japan might have had four Yamato-class battleships, three large carriers, and a handful of light carriers and cruisers completed. There would also be older ships, like the Kongo class, Hyuga, Yamashiro, and Nagato.
Italy planned for nine battleships, three aircraft carriers, 36 cruisers, 142 destroyers, and 84 submarines by 1942, a very ambitious program, though unrealistic in practice. By 1944, Italy might have completed the Impero and possibly two carriers but many of the planned cruisers would stay incomplete. The fleet would further be composed of the Littorio-class battleships and the Duilio and Cesare ships.
The navy of the United States, short of the war which hurried the construction, would have had a most gradual development; and in 1944 the United States would not have had anything afloat but the two North Carolina-class and the four South Dakota-class battleships authorized before 1939, and would have had no such swelling of the fleet as the Two-Ocean Navy Bill provided for.
France’s probable fleet would be two Dunkerque-class and four Richelieu-class battleships, with the first Alsace-class not completing until 1946. The fleet would also include two Joffre-class carriers and some cruisers; many old dreadnoughts would be retired.
Originally intended to be a class of powerhouse machines like capital ships, or battleships, the construction of the Lion class was shelved as wartime priorities shifted to smaller ships. With heavy and better-ranged armament, the Lions were to dominate and lead the Royal Navy’s battle line. Yet, the wartime demands in shipbuilding and changing naval strategies would eventually consign this program for further battleship construction to the dust.
Thinking over the postwar period, all of the relevant dynamics of naval warfare had shifted, and the great lethality of the battleship had become rather irrelevant in naval history. The Lion-class, had they been completed, would have been formidable but ultimately obsolete in the face of evolving naval warfare.
In conclusion, the force structures of 1944 in a WWII outbreak would have looked vastly different, with many ships still in planning, incomplete, or abandoned. For the Royal Navy, this would not involve an immense collection of vessels but rather new constructions, including an aircraft carrier in the Illustrious class and the Vanguard. It brings home how timing and strategic priorities influenced the overall development of the fleet in those turbulent early years of the 20th century.