Downing, T. (2015). Secret warriors: The spies, scientists and code breakers of World War I (First hardcover edition.). Pegasus Books.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रDowning, Taylor. Secret Warriors: The Spies, Scientists and Code Breakers of World War I. First hardcover edition. New York: Pegasus Books, 2015.
एमएलए (8वां संस्करण) प्रशस्ति पत्रDowning, Taylor. Secret Warriors: The Spies, Scientists and Code Breakers of World War I. First hardcover edition. Pegasus Books, 2015.
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