John Toland suggested an interesting theory: He theorized that FDR decided to allow the attack on Pearl Harbor because he was told by Navy Intelligence that only two Japanese carriers were headed to Pearl Harbor, not six carriers, and because he accepted the then-common belief that Pearl Harbor was nearly an impregnable fortress and that Japanese military capabilities were substandard. In other words, FDR believed that the Pearl Harbor attack would result in limited damage and loss of life and that this would be a small price to pay to awaken the American people to support entering the war.
This agrees with what Admiral Ranneft said. He said Navy Intelligence was tracking a Japanese fleet that included two Japanese carriers heading toward Pearl Harbor. By the way, Admiral Ranneft's son confirmed that his father told him about American Navy Intelligence showing him a map a few days before the attack that showed a Japanese fleet with two carriers headed toward Pearl Harbor (
http://www.upi.com/Archives/1982/03...efore-it-attacked-Pearl-Harbor/5562384066000/).
We know from Secretary of War Stimson's diary that FDR was looking for a way to provoke the Japanese into firing the first shot without suffering too much damage. After a 25 November White House meeting, Stimson wrote in his diary that "“The question was how we should maneuver them [the Japanese] into firing the first shot without allowing too much danger to ourselves.” So we know for a fact that as of 25 November, FDR and his cabinet were talking about way to provoke the Japanese to attack but to attack in such a way that would not do enormous damage.
Speaking of provocation, Stimson's diary entry helps us to more clearly see FDR's motive in his 1 December "three ships" order in which he ordered Admiral Stark to order Admiral Hart to send out three small ships into the path of Japanese naval task forces heading south. As many scholars have shown, the cover story that these three small vessels were to conduct reconnaissance is ludicrous. One of the vessels didn't even have adequate communications gear on board and could not have relayed recon information even if the entire Japanese fleet had stopped in front of it. FDR was hoping the Japanese would fire on one of these small ships and give him his desired excuse to declare war on Japan and thus drag America into the war and save Stalin from Hitler.
Ranneft's account raises an interesting question: Did only two of the six carriers in the Hawaii Operation break radio silence?