Same as to the IJA. The brutal fighting to the death at Guadalcanal and Papua New Guinea came as quite a shock. And we just passed the 70th anniversary of Tarawa where the Japanese very nearly did literally fight to the last man.
A. From Jonathan Daniels (son of former Secretary of Navy Josephus Daniels), an adminstrative assistant to FDR, regarding Pearl Harbor attack:
"The blow was heavier than he (sic FDR) had hoped it would necessarily be ... But the risks paid off; even the loss was worth the price. ..."
The Aspirin Age: 1919-1941, Isabel Leighton (editor), New York, NY, 1949, page 490.
B. On those "lost carriers" - First Air Fleet is placed at:
" ... Five days previously Captain Eddie Layton, Kimmel's radio intelligence officer, had reported he had no information on Japanese Carrier Divisions 1 and 2. They had mysteriously disappeared from Hitokappu Bay a week before and hadn't been sighted since. ..."
From But Not in Shame - The Six Months After Pearl Harbor, John Toland, Ballantine Books (division of Random House), New York, NY, 1961, page 36.
FYI - Hitokappu Wan (has several names) is located approximately at 45 degrees North, 147 degrees East. This positioning is not supportive of any movement south. Via Google Earth - that long straight thing is the runway of a Russia (built in USSR times) interceptor base.
C. A quick scan, Giddy Minds and Foreign Quarrels by Charles Austin Beard, from 1938, Harpers. Or, with the economic mess that the US is in, deflect that with a war ...