If the G3 battlecruisers reached service

How could completed G3 battlecruisers be rebuilt for the 1950s or 1960s?

They probably would not last that long, but their construction would transform carrier conversions, treaty ceilings, and later battleship design.

Completed G3 battlecruisers are unlikely to survive into the 1950s or 1960s in this scenario, but their construction would change the fleets that followed them. Courageous and Glorious might never become aircraft carriers, while delaying the treaty long enough to complete the G3s could also allow substantial progress on the N3 battleships. A treaty framed around ships approaching 50,000 tons would permit much larger replacements in the 1930s. Britain would have G3s and N3s instead of Nelson and Rodney, and rival navies would have to respond to that battle line. N3s with 18-inch guns would also make a later British battleship armed with 14-inch guns difficult to justify. One suggested alternative is a King George V generation with twelve 16-inch guns in four triple turrets.