Some introductory discussion points while John3rd reviews his material:
According to Conways, the original Omaha design work was done in 1915-16, and funds voted as part of the 1916 building program, as scout cruisers that would be superior to the then building RN Centaur class*. The 1916 program was suspended in 1917 to prioritise ASW escorts, with the ships completed post war.
[*which they were, the Centaurs carried only 5 x 6", were smaller and 6 knots slower; the Omahas had better armour protection. Centaur & Concord were scrapped in 1934/35; the various C-class ships of the subsequent Caledon, Ceres, & Carlisle subclasses in the OOB were not greatly different, and 8 of the 12 extant in 1941 were converted to CLAA, mostly before 1940.]
The Omaha design was reviewed as a result of wartime experience at at time when the transition from casemate guns to turrets was gathering speed, and they ended up with a bit of both, with twin turrets in A and Y locations, and four casemate guns on each side, double stacked fore & aft, so it had 8 gun broadsides, and 6 guns each could train fore & aft. The aft lower casemate guns were landed in 1940/41 and the apertures faired over to save weight, and because the lower casemates were very wet and often inoperable as a result, reducing the effective armament to 10 x 6". Conways also indicates that it was intended to replace those two guns with one gun in an open mount on the centre line aft, but this "programme ... was incomplete in 1941". Forward casemates were also landed later in at least one ship, Detroit. Conways (p120)has a sketch of Detroit in 1944 showing only one forward casemate, albeit it appears they landed the upper casemate, not the lower, one expects to make weight for more AAA weapons; possibly a 'çaptain's call'. Likewise the lower deck torpedo tubes were later landed, and the launching hatches faired over. The originally included mine-laying capability was dropped after the ships were commissioned. They were designed with scouting aircraft catapaults from the outset.
Other alternative designs that were considered were:
Original design, 1915 - had 10 x 6", 8 in the casemates, two open mounts deck level amidships, no turrets, and a minelaying capability (224 mines), 4 torpedo tubes - two twins firing out hatches from the deck below. Two triples above deck were added later.
February 1916 General Board small BC proposal - replace main armament with 2 single turreted 14" guns, reminiscent of the RN Courageous & Glorious as originally designed. BurConsRep accordingly prepared "design 160". A very bad idea, and not taken up.
October 1920 Bureau of Construction and Repair re-design- (eight ships still building) - re-arrange the armament in 4 twin centre line turrets, AB/XY (like the later RN Leander class). A really good idea, would have fixed a lot of weight problems while maintaining broadside, rejected due to funding constraints.
1921 - a derivative with 4 x 8" guns in two turrets to out-match the armament of the RN Hawkins class; this design was enlarged to the Pensacola class, and was taken to the Washington conference and set the parameters for the 'ÇA' treaty cruiser adopted there, although the CA designation was not applied until 1931.
The October 1920 design was retained as the "next" CL design, but none were ever built as the money and tonnage was devoted to the treaty cruiser - CAs. Ultimately the much more modern Brooklyn design was adopted instead.
"You may find that having is not so nearly pleasing a thing as wanting. It is not logical, but it is often true."
- Cdr Spock