Japan shifted Attu's garrison to Kiska between August and October 1942, leaving the island unoccupied while American planners still treated it as held. A later Japanese force of about 2,900 returned, fortified the island, and eventually faced roughly 15,000 American troops. The missed interval distinguishes codebreaking capability from actionable operational knowledge. If the vacancy had been recognized, a small destroyer-borne force with Marines, supplies, and Seabees might have changed the campaign before the defenses hardened.
Notable Point · 1:11:28-1:14:27
Attu's empty window and the intelligence gap
Attu stood empty for weeks, but the United States did not know in time to exploit the chance before Japan returned with a larger garrison.