But Roosevelt and most interventionists considered Japan a minor enemy- thus, the 'Germany First' Policy.
Plus, how much increase in naval expenditure could Roosevelt approve before the US public started to raise eyebrows?
There are two 'risks' here: either wake the American monster, and hope you incapacitate enough of the American Navy at Pearl Harbor, or accept the 5-10% likely loss of oil convoys from the DEI.
The entire U.S. building program was ALREADY approved.
The 1940 Two Oceans Navy Act (Vinson-Walsh Act) passed in the Summer of 1940, after Hitler put the fear of God into the U.S. Congress. It approved the construction of:
7 fast BB (two additional
Iowas and five
Montanas)
18 (!) fleet carriers
27 cruisers
115 destroyers
43 submarines
15,000 aircraft
$50 million for light patrol vessels
$65 million for munitions
This was on top of the authorization from the Navy 1938 for the construction of 135,000 tons of capital ship construction (that turned into four
Iowa class BB), 68,754 tons of new cruiser tonnage to a total of 412,000 tons, 38,000 tons of new DD tonnage up to 228,000 tons and the 1934 & 1936 Navy Acts that had approved six new fast BB (the
North Carolina and
South Dakota classes).
The USN that pureed the Japanese fleet was 100% approved and funded by 1940. That was WHY the Japanese attack the U.S. as soon as they had the six decks available that the attack plan required (
Zuikaku finished an abbreviated shakedown cruise on November 7th, on November 18th she sail into Hittokappu Bay to join the strike force). Japan was on a short clock and knew it.