At 1:28 a.m. on December 7, 1941, a secret United States Navy radio station, Station S, Bainbridge Island, intercepts a message from Tokyo to the Japanese embassy in Washington, D.C. The message instructs the Japanese ambassador to break off ongoing peace negotiations with the United States, but its secret purpose is to alert the ambassador that Japanese forces are poised to attack Pearl Harbor.
Station S had been intercepting Japan's diplomatic radio messages since 1939, when the U.S. Navy moved its listening post at Fort Stevens, Oregon, to Bainbridge Island. In its new island home, the facility opened as the Communications Support Activities (COMSUPACT) at Fort Ward, a former coast artillery post.
A year later, in 1940, COMSUPACT was renamed Station S, Naval Security Group Activities (NSGA). Along with eavesdropping on and recording Japanese diplomatic radio messages, Station S served as a control station for radio direction tracking of Japanese merchant shipping. The station collected radio bearings from two or three other stations, allowing the radio direction finding to identify the positions of Japanese ships.
In November and early December 1941, Japan's diplomatic messages increased, and Station S worked harder to intercept the heavier traffic. Commander B. C. Purrington (1896-1961), the station’s commanding officer, noted increased shipping activity in his November and December 1941 secret station reports to the chief of naval operations. The radio traffic and messages indicated that something was happening, and this activity intensified between December 4 and December 6, 1941.
A Fateful Message
The fateful message Station S intercepted in the early morning on December 7 was to be delivered to the U.S. Secretary of State in Washington, D.C., at 1 p.m., just before the attack on Pearl Harbor was set to begin (it started at 1.20 p.m. Washington, D.C., time). However, delays in translating the message prevented its punctual delivery.
Although the the message and other intelligence pointed to possible war, American intelligence officers did not anticipate the attack on Pearl Harbor. On December 7, 1941, the Empire of Japan bombed Pearl Harbor, located in Hawaii. American losses amounted to eight battleships, three destroyers, three light cruisers, four auxiliary craft, 188 airplanes, 2,403 deaths, and 1,178 wounded. On the following day, December 8, 1941, the United States declared war on Japan.