Meanwhile, on May 29, seaplane tender (destroyer) USS ''Thornton'' (AVD-11) arrived at French Frigate Shoals to relieve light minelayer USS ''Preble'' (DM-20) on patrol station there. The presence of U.S. ships at French Frigate Shoals prevented the Japanese from refueling flying boats to reconnoiter Pearl Harbor. Although the Japanese could not visually confirm the departure of Task Forces 16 and 17 from Pearl Harbor, American preparations to defend Midway were on the verge of discovery anyway. Japanese COMINT stations not only learned of carrier movements in and out of Pearl Harbor, simply by listening to increased air-ground radio chatter, but traffic analysis of "Urgent" American radio messages coming out of Pearl Harbor suggested at least one Task Force was at sea. Incredibly, these discoveries by Japanese COMINT were withheld from the Midway Strike Force because of Yamamoto's strict radio silence restrictions. | Meanwhile, on May 29, seaplane tender (destroyer) USS ''Thornton'' (AVD-11) arrived at French Frigate Shoals to relieve light minelayer USS ''Preble'' (DM-20) on patrol station there. The presence of U.S. ships at French Frigate Shoals prevented the Japanese from refueling flying boats to reconnoiter Pearl Harbor. Although the Japanese could not visually confirm the departure of Task Forces 16 and 17 from Pearl Harbor, American preparations to defend Midway were on the verge of discovery anyway. Japanese COMINT stations not only learned of carrier movements in and out of Pearl Harbor, simply by listening to increased air-ground radio chatter, but traffic analysis of "Urgent" American radio messages coming out of Pearl Harbor suggested at least one Task Force was at sea. Incredibly, these discoveries by Japanese COMINT were withheld from the Midway Strike Force because of Yamamoto's strict radio silence restrictions. |