The 12in disaster of LNT aka Admiral William Daniel Leahy's 12in LNT

[Tzoli]

I've posted this on another forum but I post it here as well if it can get some thought processes flying:

From Norman Friedman's US Battleships - An Illustrated Design History:

By this time the United States had been committed to achieving naval parity with Britain for about fifteen years. Acceptance of the 12-inch gun limit would preclude parity until after the demise of the Nelsons (1951, if proposed twenty-six-year lifetime were accepted). Leahy's proposed alternative was not merely to limit new construction but also to require that existing guns replaced by 12-inch weapons on a one-for-one basis - which would overwhelm the British, as their eight-gun ships would face US units armed with twelve guns (originally 14 inch vs. British 15 inch).* Studies already showed that the alternative, for 12-inch ships to face the 16-inch Nelsons, would be as ruinous as the situation of the wooden ships at Hampton Roads exposed to the Merrimack before the appearance of the Monitor. At 20.000 yards, a 12-inch shell would penetrate only 9,6 inches of belt and 2,4 of deck, compared with 15 and 3,4 for the 16in/45. Leahy clearly considered the regunning proposal a bargaining tactic to be used at the coming London Conference, "It would be very pleasing to me if the US could get an advantage t one of these conferences." He found it particularly unfortunate that the public not understand that the British system of overseas bases unbalanced any apparent equivalence between the two navies achieved by treaty.

* It was argued that 16-inch guns could be replaced by larger numbers of 12-inch guns: three for every two US 16-inch. Quadruple turrets were considered impractical, so there was the delicious possibility of Nelsons armed with nine 12-inch facing Colorados armed with twelve such weapons.

So... the question arises, how would WW2 look like if 12" armed battleships would roam the oceans? Both older re-gunned ones with thick belt armour for their calibre and new ones with corresponding belt armour for their calibre? What would be the implications of such an under-gunning present?
Or just imagine 4x3 12" armed Colorados VS either 3x4 or 3x3 12" armed Nelsons and 4x3 31cm armed Nagatos?

Of course the question arises if the old guns were to be scrapped, to be used as coastal defence or "stored"? If stored we could except re-gunning to the original calibre in the first few months of any war and thus would reduce the capital ships of each nations in the early parts of the war due to the re-installment of the original weapons.

 

[lancer21]

Wanted to add couple of thoughts on this ATL, imo it is extremely unlikely that the main navies would accept such a radical proposal for the ships already in service, not in the least because it will be hugely expensive to replace all those hundreds of barrels. And for instance the RN of course would realize the kind of disadvantage they would be at in a 1 to 1 replacement scheme.

What is more likely to happen imo is accepting the 12 in limit for the new build ships after the LNT. So we probably could have KGVs and US 35,000 tonners with 12 x 12 inch guns, good for perhaps 30 knots or more.
Does Japan still leaves the treaties? It might depend on them staying or leaving whether any 12 inch ships are build in the first place.
The germans are as OTL until the Bismarcks, which may have 12x 28cm guns.
The frech put 8x 305mm guns on the Dunquerkues, and perhaps 12 on the Jean Barts.
The italians don't rebore the 305mm guns on the old modernized BBs, and perhaps put 12 x 305mm guns on the Venetos.
Etc. etc.

It is of course very likely there will be a lot of cheating going on, probably the japanese even if they build 12 inch Yamatos they will have secret provisions to upgun them later, same with italians, germans, french etc. The japanese might build something like the B-65 but with 12 guns, and likely with provisions to mount 8x 36 cm instead, or even 8x 41 cm leftovers from the 8-8 plan.

One advantage of 12 inch ships is that they would be easier to keep within 35,000 tons, so the ships are more economical. The guns will presumably fire a lot faster than the bigger/older guns so they can lob a lot of shells at the older opponent in a given time. They will probably go for at least L/50 guns, maybe even more if feasible, to give them the maximum possible range/penetration. It's quite possible they might even carry TTs, to be sure of being able to kill the older BBs. Also they will be fast, at least 30 kts or more.

 

[Tzoli]

1:1 was never considered except maybe for the later 14" armed US battleships with their closely spaced barrels. They just did not want quad turrets, but other navies might consider them strongly so will the USN as evident of the North Carolinas some 5 years later. In this timeline we might see various turrets designs to cram in the maximum barrels in the space of the old turrets.
Possibilities: 2-gun, 3-gun, 4-gun, twin, triple, quad variants: 2-2 (double twin) 1-2-1, or even experimenting with elevated turrets.