Takeo Yoshikawa - His Spy Charts Used in Pearl Attack

Takeo Yoshikawa was known as "Tadasi Moriumura" to everyone but the Japanese Imperial high command.  That's because he had a specific job to do at the Pearl Harbor Japanese Consulate - and it wasn't doing consulate work.

Tasked with helping pilots (who had never been to Pearl Harbor) find their individual targets, Yoshikawa created very detailed information and charts.  Without his input, the surprise attack would have been less deadly - or may never have occurred (as noted in "Japanese Spy at Pearl Harbor," by Jules Archer:

As Japanese planes roared in to put the finishing touches to America's worst defeat, Takeo Yoshikawa swelled with pride.  For he, and he alone, had been responsible for the success of the infamous sneak attack.

If anyone had paid attention to all of his "comings and goings," perhaps the spy would have been caught.  Such, however, was not the case - as observed in And I Was There:

Our ONI and FBI agents might have been more suspicious about the role the counsel was playing if they had paid more attention to the peripatetic journeyings of his energetic third secretary, Yoshikawa, alias Morimura.

Credits

First quoted passage - from "Japanese Spy at Pearl Harbor," (pages 72-77) by Jules Archer, in WWII Journal #2 - Pearl Harbor.

Second quoted passage - from "And I Was There" Pearl Harbor and Midway - Breaking the Secrets, by Rear Admiral Edwin T. Layton, USN (Ret.), with Captain Roger Pineau, USNR (Ret.) John Costello.