Why did the Two-Ocean Navy Act include 18 carriers?

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The reason for the difference, beyond the fact that even in 1940 the future was clearly in the air, is that the carriers were

1. Lighter in tonnage and Congress approved ship types by tonnage.

2. Less costly to build. Iowa & her sisters were $125,000,000 (in 1942 dollars!) per unit. Each Essex was ~$65,000,000.

The Two Navy Act authorized specific ships, though.

I think the reason is that we had enough BBs built or under construction, and that the battleship-orientation of the navy is largely mythological. We were fully aware of the utility of carriers and their power, and we didn't have enough for Orange, let alone a potential European front.

In 1940 we had, besides the older ships, 2 North Carolinas, 4 South Dakotas, and 4 Iowas under construction. With two more Iowas and 5 Montanas, we would have had twice the battleship power of all the Axis powers combined, not to mention we had the RN on our side.
 
The navy had already prepared war plans against Japan (e.g. war plan orange) and had in the 30ties tried to build fast and large cruisers, mainly to move quickly in the pacific and to control it against Japan. Chosing (18) carriers instead in 1940 is just replacing the control- and reconnaisance-capability of cruisers by carriers and planes. And - of course, carriers and planes could be built and delivered quicker than the heavy guns for battleships and cruisers. So, it is more "carriers instead of cruisers" than "carriers instead of battleships". This dates also back to the 1930 and 1936 naval conferences in London where the ratio US:GB:JP for cruisers was changes to Japans favor from 10:10:6 to 10:10:7 -
and even in 1938 the USN had only 34 cruisers against Japans 36.
(The 1940-naval-act included 27 cruisers, less than what the Navy had asked for in the previous years)
 
we had to wait almost a year to hear it? So obvious. Like Lehmann wrote, the naval treaty tonnage allowed only so much per country "in the name
of Peace". Therefore any lighter power packing solutions were at a premium,
and carriers even by that date were it. This international weight agreement
is in just about every history book.
 
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