Patreon 68: What if the Royal Navy went 4.7in rather than 4.5in for dual purpose?

The counterfactual begins by choosing the earlier 4.7-inch 45-calibre family, whose existing mounts offer a more practical route to high-angle fire than the later 50-calibre weapon.

Only imperfectly: a shell from one system might theoretically fit another in one direction, but the reverse was unsafe and a proper common round would require further development.

Exercise assumptions and the expected bomber threat preserved the 4.7-inch gun as a low-angle destroyer weapon while the 4.5-inch programme grew from replacing four-inch AA guns.

Several: Vickers-Armstrong participated alongside other private firms, naval organizations, and nationally owned gun foundries.

Only to a limited extent: ships could carry much heavier mountings and used moving guns to disrupt incoming formations, while land forces defended fixed positions with different weight and operating constraints.

Making 4.7 inch the common dual-purpose calibre would affect destroyers, sloops, cruiser conversions, and new ships historically armed with four-inch or 4.5-inch guns.

Cruiser and capital-ship status pushed designers toward a gun larger than the destroyer's weapon, even though a five-inch system had originally been preferred.

No. The British 4.7-inch was about 120 mm and the 5.25-inch about 134 mm, while roughly 5.1 inches corresponds to 130 mm.

Weight limits made a useful armoured turret impractical; an open-backed shield could provide splinter protection without trapping the crew in a thin-skinned enclosure.

The relevant 4.5- and 4.7-inch projectiles were close enough in weight that funding, shell design, muzzle velocity, and mounting elevation mattered more than a nominal five-pound difference.

The main wartime change replaced the after 4.7-inch mounting with a twin four-inch high-angle mounting because the original main battery could not elevate far enough for air defence.

A mount reaching roughly 80 degrees could keep firing as a diving aircraft closed, unlike the 50-degree destroyer guns that left a dangerous gap near the ship.

Not by itself: the answer depends on the particular 4.7-inch weapon, and the chosen 45-calibre family already evolved toward cartridges but still needed better shell ballistics and funded development.

The alternate 4.7-inch programme gains its timing advantage from modifying an existing upper-deck mount rather than waiting for the delayed 4.5-inch destroyer installation.

No. Their apparent roles emerged from programme history: the 4.5-inch began as a four-inch replacement, while the 4.7-inch remained low-angle until wartime exposed the need for a destroyer high-angle weapon.

Not to any important degree in this case; Britain had several very large arms manufacturers and enough domestic expertise to develop the weapon itself.

The specific marks discussed entered service around 1930, while their technical family reached back to a 1918 weapon rather than to unrelated 1880s guns of the same nominal calibre.

Applying the common-calibre assumption to the very fast Abdiel-class minelayers produces a striking surface-warfare consequence as well as better air defence.

A common 4.7-inch family could simplify wartime supply, but achieving 80-degree elevation would still demand a carefully balanced redesigned mount.

Fighters, heavy flak, manoeuvre, and 40 mm weapons form a layered system; high-angle guns matter because they keep disrupting an attack until it reaches the close-range screen.

Existing four-inch weapons could move to trawlers and other auxiliary craft, while the failed five-inch system and the superseded 4.5-inch programme would not create comparable stocks.

A high-angle Tribal battery blurs the line between destroyer and AA cruiser, raising questions about Dido construction, C-class conversions, and wartime production priorities.

The available 4.5-inch production was already demanded by new capital ships and aircraft carriers, leaving little capacity for a lower-priority refit.

Canadian and Australian production could spread a dual-purpose Tribal programme, but propulsion machinery rather than hull-building capacity remains a major constraint.

The 4.5-inch upper-deck mounting entered development late, was repeatedly deferred in pursuit of a better solution during wartime, and did not mature until the Daring class.

They were close enough to be credible peers if Britain redirected the money spent on the 4.5-inch system into improving the established 4.7-inch gun, ammunition, and mounting.

Probably: if the 4.7-inch replaced the four-inch and 4.5-inch programmes, new cruisers from roughly 1936 onward would likely be designed around it, though not every older ship would necessarily be converted by 1939.

No. Dive-bombing already existed, but the Air Ministry promoted level-bomber assumptions and exercises repeatedly directed aircraft at capital ships rather than their destroyer escorts.

In Norway, high-angle destroyer batteries could keep Gurkha inside her formation, strengthen mutual support, protect transports, and impose greater losses on experienced German aircrews.

The navy wanted to retire the ships, disliked the 7.5-inch system, and retained the class mainly because no immediate replacement could cover its role.

A worked Mediterranean example shows that enabling every destroyer's main battery to fire at high angles could raise a task group's steep-angle gun count from roughly 32 to 93.

Usually not on ships already designed for 4.7 or 4.5 inch, but conversions from four inch could require fewer rounds or rearranged storage and might justify retaining the smaller weapon.

Operation Claymore supplies a concrete force comparison: a universal 4.7-inch battery could more than double the destroyer group's guns able to engage through the full high-angle arc.

A layout comparison explains why wartime radar and light-AA additions strained Dido-class cruisers while Tribal-class destroyers retained more useful margin.

Repulse's 1933-36 refit could replace separate surface and AA four-inch batteries with six twin 4.7-inch mounts able to serve both roles.

The counterfactual cannot freeze Axis tactics: heavier British AA losses could accelerate stand-off guided-bomb programmes and change the threat by 1942 or 1943.

Force Z's fate changes through a cumulative chain involving surviving escorts, carrier availability, fighter coordination, ship manoeuvre, and Japanese luck. The gun alone is insufficient.

They were reused on destroyers still moving through production rather than automatically being scrapped or transferred to merchant ships.

The 4.7-inch shell was large enough for a proximity fuze, and its wider fleet distribution would let the Royal Navy extend the new capability to more ships quickly.

No. Courageous and Glorious were lost to submarine and surface threats, while Ark Royal's loss turned on damage-control failures that a better AA battery would not correct.

No. A historical-statistics table gives 259 million for public administration and defence against GDP of 4,932 million, far below 50 percent.

Converting the fleet during wartime would impose an enormous logistical and industrial burden, while British industry was capable of developing a suitable domestic weapon from its existing 4.7-inch base.

A production discussion separates the rapid assembly of an open destroyer mount from the manufacture and delivery of an enclosed capital-ship turret batch.

Possibly: fighters remained available, but a message that bomber and reconnaissance support was unavailable was understood as meaning that no air support could be requested.

The closing argument links the feasible 4.7-inch alternative to a broader lesson: war scales mature designs more readily than it invents complex new systems from scratch.

The Battle class illustrates how a ship programme could be delayed by dependencies on both American fire-control equipment and the British 4.5-inch installation.

No. It could reduce naval losses, but it could not repair the ground-command, staffing, and logistics failures that determined those campaigns.

The closing discussion connects Singapore's reservoir, Japanese supply exhaustion, and a delayed scorched-earth decision to the campaign's ground-level turning points.