OOC:How many OTL ships would the US Navy have to sacrifice to get the extra Iowas and the Montana?
A lot, it's not the steel, but the time spent in large slips in the yards.
A single Essex generally took about a year in the slips, a single BB about 30 months.
Norfolk NSY built CV38 and CV40 in the time Kentucky would have been in the yard.
If Illinois was laid down right after NJ came out, then Philly NSY would not have built CV36 and CV45.
If NY NSY lays a Montana down after Iowa, CV20 and CV33 are gone
If Newport News lays down a second Montana after BB58, then CVs 10, 14 and 32 are lost.
That's 9 Essex class sacrificed for 4 extra BB hulls, most of which will not be commissioned before 45 because they require ~3 1/2 years from keel to commissioning. Any BB class ship laid after Jan42 will not see service before mid 45, and more likely 46. Missouri was laid Jan41, was launched in Jan44, and commissioned mid 44, while not actually arriving in the Pacific for action until Jan45. Lay down a BB hull one year later, it won't see the war at all.
Essex hulls averaged 20 months between keel and commission, with Newport News schooling everyone on building Essex class, commissioning CV13 and CV14 in 13 and 14 months respectively. The Naval Shipyards dragged down the average construction time while Newport News and Fore River knocked them out.
I time-lined out 32 Essex class commissioned by end 45 if the last 2 Iowas and all the Alaskas were not built. Two in 42, 12 in each of 43 and 44, and 6 in 45. In OTL 14 Essex were commissioned by the end of the war, I can commission 14 by the end of 43, along with 6 CVLs in 43.