Pardon me if someone has covered this; I didn't see anything last I looked, and I've just been glancing over a few things in Friedman's work to look at the period designs.
As for competing nations, it depends on what time that the the British notify the other nations that they will proceed.
The US considered several design studies in 1928-1929, but only resumed in 1931 any serious continuation of design specimens. Correct me if I'm wrong, but it's likely that such a decision would be made in 1930.
Given that, the General Board parameters would likely be the ones from that same period. The first US battleships would retain their turboelectrics. Due to economy, 16" guns would likely be used so that existing 16" turrets from the South Dakota class would be used on them, thus leading to 3x3 16" guns. There were several design studies for the time that attempted to reconcile the need for reducing weight and maintaining firepower and armor. There is an interesting broken forecastle, with the #1 turret on the same deck as the #3 turret on one plan. That is in the standard ABX arrangement for those. There are also several plans for Nelson style designs, though the C turret would always be superfiring on these designs (the B either on same deck as A, or A sunk a deck lower on a broken forecastle. The US General Board did not care for these designs as they worried about a catastrophic hit eliminating all turrets, and did not share the same desire to shorten the armored belt to take as much of an advantage as the British did.
Scheme D in Oct 1928, a conventional design of ABX turrets, with turboelectric and with a monstrous endurance of 20k nm at 10 knots, would only be able to carry 8 guns in two triples and one twin superfiring.
Your secondary armament would likely be the 6"/53 in twin mounts, likely improved from the Omaha variant of the mount for better reload. Here, they'd be placeholders for DP guns, as what became the 5"/38 is still under development at this time, and the board was favorable to twin mounts vice multiple single mount DP guns likes on older vessels.
Other than that, space was allotted for 10 smaller caliber AA guns. Provisions for 4 aircraft and two catapults were planned on all battleships. The catapults would be the cross-deck variety but on the quarterdeck (vs midship on British vessels).
Machinery as mentioned would be turboelectric. Speed would be in the 21-23 knot range. The 16"/50 on the South Dakota class would demand enough weight that it'd be likely be traded for the 16"/45 (the 16"/50 designs tended to have short belts of 12' vs the 16' 6" of the 16"/45 design belts).
So, for your first two ships ordered, they'd likely be variants of one of the above and would likely appear similar to a slow, turboelectric version of OTL North Carolina. Perhaps call them the Slowboat (Vs NC's Showboat). They'd effectively be an improved Colorado class. After C & D are ordered, you'll see the US starting to look at larger changes, perhaps leading to geared turbines and similar.
I imagine most future designs will be devoted to maintaining superiority in firepower vs British vessels individually while also slowly changing to combat the Japanese designs.
As for competing nations, it depends on what time that the the British notify the other nations that they will proceed.
The US considered several design studies in 1928-1929, but only resumed in 1931 any serious continuation of design specimens. Correct me if I'm wrong, but it's likely that such a decision would be made in 1930.
Given that, the General Board parameters would likely be the ones from that same period. The first US battleships would retain their turboelectrics. Due to economy, 16" guns would likely be used so that existing 16" turrets from the South Dakota class would be used on them, thus leading to 3x3 16" guns. There were several design studies for the time that attempted to reconcile the need for reducing weight and maintaining firepower and armor. There is an interesting broken forecastle, with the #1 turret on the same deck as the #3 turret on one plan. That is in the standard ABX arrangement for those. There are also several plans for Nelson style designs, though the C turret would always be superfiring on these designs (the B either on same deck as A, or A sunk a deck lower on a broken forecastle. The US General Board did not care for these designs as they worried about a catastrophic hit eliminating all turrets, and did not share the same desire to shorten the armored belt to take as much of an advantage as the British did.
Scheme D in Oct 1928, a conventional design of ABX turrets, with turboelectric and with a monstrous endurance of 20k nm at 10 knots, would only be able to carry 8 guns in two triples and one twin superfiring.
Your secondary armament would likely be the 6"/53 in twin mounts, likely improved from the Omaha variant of the mount for better reload. Here, they'd be placeholders for DP guns, as what became the 5"/38 is still under development at this time, and the board was favorable to twin mounts vice multiple single mount DP guns likes on older vessels.
Other than that, space was allotted for 10 smaller caliber AA guns. Provisions for 4 aircraft and two catapults were planned on all battleships. The catapults would be the cross-deck variety but on the quarterdeck (vs midship on British vessels).
Machinery as mentioned would be turboelectric. Speed would be in the 21-23 knot range. The 16"/50 on the South Dakota class would demand enough weight that it'd be likely be traded for the 16"/45 (the 16"/50 designs tended to have short belts of 12' vs the 16' 6" of the 16"/45 design belts).
So, for your first two ships ordered, they'd likely be variants of one of the above and would likely appear similar to a slow, turboelectric version of OTL North Carolina. Perhaps call them the Slowboat (Vs NC's Showboat). They'd effectively be an improved Colorado class. After C & D are ordered, you'll see the US starting to look at larger changes, perhaps leading to geared turbines and similar.
I imagine most future designs will be devoted to maintaining superiority in firepower vs British vessels individually while also slowly changing to combat the Japanese designs.
