Because the screw up was fixed before it caused any construction delays, it does not feature prominently in the story of these ships. But the incident is a comedy of errors, the perfect example of how government bureaucracies can be incredibly efficient, and create tremendous finished products individually, yet be so stuck inside of their own silos that the end result is substantially LESS than the sum of its pieces.
The story starts with the cancellation of the BB-49 class battleships and CC-1 class battlecruisers. The US Navy's Bureau of Ordinance (BuOrd) came up with a wonderful 16-inch weapon for them, the 16/50 Mark 2. Great range, solid steel (not wire wound), good accuracy, great armor penetration. The Naval Gun Factory cranked them out at such a rapid pace that when the ship were canceled per the Washington Treaty there were already 71 complete and 44 semi-complete guns on hand. The US Army asked for some for coast defense, so 20 were turned over to them, but the rest went into storage for future use
The General Board worked within the 35,000 ton treaty limit, and was quite happy with the South Dakota Class design. The Bureau of Construction & Repair (we'll call the C&R for short) came up with a fine ship design. But because of the weight limit, both the South Dakota and North Carolina Class battleships needed a new, lighter weapon than the 16/50s in storage. So BuOrd came up with the 16/45 Mark 6. It was substantially lighter and smaller around, plus the barbettes were smaller around and the turrets were smaller/ lighter. Although it lacked the range and hitting power of the 16/50 it was an excellent weapon.
When it looked like the treaty limit would jump up to 45,000 tons, the General Board went looking to see what they could 'buy' with the extra 10,000 tons. The first basic idea was to use the basic South Dakota design, stretch the hull, and add another turret. This would give a nice increase in hitting power. But the fleet wanted some fast battleships to build fast task forces around with carriers and cruisers, as the Japanese could do this with heavy cruisers and the Kongo class escorting carriers. So the other basic idea was a South Dakota with a stretched hull to fit more machinery, to give a 6 knot speed increase. This sounded like a fine idea, but the General Board thought that surely 10,000 tons would get them more than just a speed increase: could they not have an increase in hitting power also?
So the final idea was what would become the Iowas Class: stretch the hull for more machinery and speed increase to 32 knots, and fit the 16/50s from storage for an increase in hitting power without increasing the number of main guns. Sounds perfect, right?
Well, on paper. When C&R drew it up, they found they would be over the treaty limit. They told the General Board that they could make it work without thinning the armor protection or cutting speed if the turrets could be made lighter. So the General Board asked BuOrd for alternate turret designs, asking them just how light a 16/50 turret could be, without really explaining why. BuOrd thought it was just a theoretical paper design exercise and made a table listing several theoretical 16/50 turret designs, the lightest being one that used the smaller barbette of the 16/45, and that basically skipped all the technological and safety advances made over the preceding 20 years, and that was too cramped to be workable in the real world- but it WAS as light as a 16/50 turret could possibly be. But the General Board passed the specs on to the C&R folks, who thought it was a done deal, and proudly said that with these turrets they could build the 32 knot ship carrying 9* 16/50 guns with the required level of protection on 45,000 tons. The General Board approved, the treaty limit did in fact jump to 45,000 tons, and all seemed well in the world. The original idea, a slower ship with a fourth turret, would eventually morph into the Montana Class design.
C&R, not knowing that the ultra-light turret was just a paper exercise and not a real BuOrd design, designed the ship around its smaller diameter barbette. BuOrd, not knowing that C&R was counting on the smaller turrets, went about designing an improved 16/50 turret with the original, larger diameter barbette they assumed C&R was designing the ship around. Both bureaus worked independently, and no one on the General Board thought to check, so both bureaus had virtually completed their design work and were ready to start contracting out the construction before anyone realized they were working on two completely different and incompatible projects.
When someone finally realized that the turrets would not fit the ship, there were three options.
The first was to modify the ship to accept the turrets. C&R looked at this, but the larger barbette diameter meant cutting larger holes in the strength deck, so the turrets had to be further apart. this pushed the A turret up the bow flair, making it higher from the waterline, so B turret had to be taller to 'see' over it, and the conning tower had to be taller yet to 'see' over B turret...the snowball effect pushed the design well above the treaty limit. Not acceptable.
The second solution was to actually make the turrets small enough to fit in the 16/45 barbette. BuOrd said this was not possible in the real world; they could only did it with the paper exercise by making unacceptable cuts in safety, equipment, and room to work the guns. So if they made the turrets fit the ship, the guns could not fit the turrets. Also not acceptable.
The third solution, and the one I think every other nation on Earth would have needed to go with, was to simply use the 16/45 guns and turrets from the South Dakota. This still would have been and excellent ship, well protected, fast, and it would have the advantage of simplified logistics with all the new battleships carrying the same gun. But this meant that all 10,000 tons gained was a jump from 27.5 to 32 knots, and the General Board had already said they wanted more than just a speed increase for the cost of the extra 10,000 tons, and since the Iowa was not even the full 6 knots faster then South Dakota they did not think this was an acceptable solution either.
But BuOrd saved the day: they surplussed the existing 16/50 guns, scrapped the turret design they had just completed, and broke out there pencils and slide rules. They quickly designed an all new 16/50 Mark 7, which had the range and hitting power of the original, but was much stronger structurally, so it could be thinner, resulting an a gun that had a much smaller exterior diameter than the original. This let them design a turrets for it that fit in the same smaller diameter barbette as the 16/45- the same one C&R had designed the ship around.
So the General Board got what they had wanted: a fast battleship with more hitting power then the South Dakota. The Naval Gun Factory was able to manufacture the guns quickly enough that there were no construction delays, even though they had not counted on having to manufacture ANY heavy guns for the Iowa Class at all. That they could unexpectedly fill the order for 36 16-inch guns (plus a prototype and several spares) of an entirely new design, and that they could do it without causing even one day of delay to the Iowa Class project, speaks volumes about what an astonishing organization the Naval Gun Factory was, and about just what a tremendous industrial capacity they had. While even the UK had to order guns more than a year before laying down the ships, the Naval Gun Factory was able to build dozens of the new 16/45 even though they got the order AFTER North Carolina was laid down, and also to build dozens of the 16/50 on short notice, both without causing any delays to the construction of the ships.
Everyone went about their business happy with the end result: catastrophe had been averted. With no one wanting to stir up a firestorm of blame that might burn them also, that was that, and there were no negative consequences to a design process that sounded like an Abbott and Costello skit. Well, no negative consequences unless you count the time wasted designing the larger turrets that ended up not being built, and the 71+44 excellent battleship weapons that the Navy was never ever actually able to use. They gave them to the Army, but they did not have much in the way of either need or funding for them, so they pretty much went to waste.
) Especially American guns were excellent.