To be completely fair about this, the US was ramping up a long time before Pearl Harbour. (This is part of the extended discussion around the attack itself, and whether it should have been anticipated.) British rearming began in 1936, the US was certainly planning in the late 30´s, actual spending began in 1939, and ramped up quickly after that during 1940.
In war, as in many other things, if you want to ride the wave, you have to be ready long before you see it coming.
In war, as in many other things, if you want to ride the wave, you have to be ready long before you see it coming.