Could Britain build a 12-gun 18-inch fast battleship in 1918?

Could Britain have built a 155,000-ton fast battleship with four triple 18-inch turrets and a 28-knot speed by 1918?

Probably: the 18-inch gun program, small-tube boilers, and very large hull studies supplied the necessary technical foundations.

The answer treats the enormous proposal as possible rather than practical. Britain already had an 18-inch gun program in progress. Small-tube boilers supplied a route toward the requested 28-knot speed, and contemporary design work showed that British yards could contemplate ships in the stated tonnage range. Those ingredients make the concept technically plausible, although the short answer does not claim that such a ship would be affordable or strategically sensible.