Why didn't the Royal Navy go for High Pressure boilers & what if they got 850psi boilers in 1934?

The treaty system and earlier fleet remain unchanged; the divergence begins in 1934 as higher-pressure machinery reshapes refits and new construction.

The Royal Navy's 300 psi Admiralty three-drum boiler suited a worldwide fleet because it was reliable, maintainable, and straightforward to build.

The boiler choice illustrates a recurring fleet problem: advanced machinery can demand specialist support, trusted technicians, and secure access far from home bases.

Higher boiler pressure can reduce fuel use and boiler count while increasing turbine efficiency, shaft power, range, or speed.

Contemporary ultra-high-pressure experiments and John Brown's turbine work make an Anglo-American 850 psi marine plant technologically plausible by 1934.

Replacing Warspite's historical six-boiler refit plant with four 850 psi boilers could plausibly yield a 28-knot Queen Elizabeth-class battleship and larger weight savings.

The new plant changes ships entering refit or construction from 1934 onward, from G-class destroyers and cruisers to Ark Royal, the Illustrious class, and King George V battleships.

Foreign responses make wartime outcomes too uncertain to project confidently, so the exercise concentrates on Royal Navy and US Navy construction choices before 1939.

The historical refit sequence gives the Royal Navy a staged route for replacing the converted carriers' First World War-era boilers and learning from each installation.

The G-class destroyers would be the first new destroyer design to test how 850 psi boilers change power, speed, range, and fuel efficiency at small-warship scale.

Barham's recently completed 1931-1934 refit makes her a poor immediate candidate for another machinery reconstruction even when the new boilers promise major gains.

The same weight and performance gains could improve the nine-gun 16-inch Lion design and make completing the class more attractive.

Replacing six old boilers with perhaps two 850 psi units could turn the C-class anti-aircraft conversion into a much more extensive machinery and weapons redesign.

Fewer boilers could give Ark Royal better protection and let Illustrious-class carriers trade machinery weight for a longer hangar and a larger air group.

Halving boiler count could release enough power, length, and protected volume for a 28-30-knot King George V carrying three quadruple 14-inch turrets.

Britain's underused heavy-turbine capacity could support a wider program that makes older battleships and converted carriers faster, longer-ranged, or better protected.

Refitting Courageous could validate the machinery arrangement intended for Ark Royal and the Illustrious class while improving the older carrier's speed, range, and weight margin.

The Royal Navy's long commitment to the three-drum boiler made a rapid mid-1930s change difficult, whereas a proven 850 psi plant available in 1934 could enter service before rearmament accelerated.

Four 850 psi boilers could give Renown more power than her historical eight-boiler reconstruction while letting designers preserve speed or deepen protection.

Town-class and smaller cruisers could use 850 psi plants for roughly 36-knot performance, longer range, or freed space for weapons and reconnaissance aircraft.

The smaller Arethusa-class cruisers and speed-centered Abdiel minelayers could exploit the new plant especially well in Mediterranean scouting, raiding, and minelaying missions.

An Anglo-American project could let Yorktown and Enterprise reduce boiler count and redirect treaty-limited displacement toward armor and torpedo protection.

If Anglo-American battleships make 28 knots the baseline, Yamato and Littorio designs may need more machinery, altered layouts, or a sharper redesign to preserve tactical speed advantages.

Fleet-wide adoption makes the prewar Royal Navy more formidable and gives Tribal-class destroyers choices between extreme power, fewer boilers, survivability, and added weapons.

The Tribal-class design could pursue extreme shaft power or use a separated two-boiler plant that still improves performance while reducing single-hit vulnerability.

Machinery savings might improve Royal Oak's torpedo defense, release other capital ships from convoy duty, and make faster Mediterranean bombardment operations more practical.

Faster and more numerous British capital ships reduce the relative threat posed by Dunkerque-class ships and a potentially hostile French fleet after France falls.

A 28-knot Queen Elizabeth-class force could approach and withdraw from Taranto faster, making a surface bombardment more plausible before daylight air attack.

The better machinery makes Nelson and Rodney candidates for modernization, but every refit consumes dockyard capacity that might otherwise build carriers or new capital ships.

Fast, long-ranged Anglo-American steam warships could quickly undermine the Deutschland class and reopen the efficiency comparison between boilers and diesels.