How G3 battlecruisers could reshape the wartime fleet

How might two or three completed G3 battlecruisers have served in and after the Second World War?

They would likely serve with fast carrier forces, influence carrier and battleship design, and might survive long enough to displace the need for Vanguard.

Completed G3 battlecruisers are placed with fast wartime formations such as Force H, where their speed and heavy armament could support carrier operations. Their presence might push the Royal Navy toward faster and longer carriers, possibly trading some armour for a larger air group. Because the G3s would still be relatively modern after 1945, they might escape the rapid disposal suffered by older capital ships. They could also reduce the need for Vanguard or redirect that construction effort toward another type. A later answer credits their internal structure with some protection against plunging fire while declining to call that protection outstanding. Treaty tonnage remains the hinge: retaining such large ships would require higher limits and would change the specifications of other British battleships as well.