Herbert Osborn Yardley was an American cryptologist. He founded and led the cryptographic organization the Black Chamber. Under Yardley, the cryptanalysts of The American Black Chamber broke Japanese diplomatic codes and were able to furnish American negotiators with significant information during the Washington Naval Conference of 1921–1922. Recipient of the Distinguished Service Medal. He wrote The American Black Chamber (1931) about his experiences there. He later helped the Nationalists in China (1938–1940) to break Japanese codes. Following his work in China, Yardley worked briefly for the Canadian government, helping it set up a cryptological section of the National Research Council of Canada from June to December 1941. Yardley was reportedly let go due to pressure either from the Secretary of War Henry L. Stimson or from the British.

Signals intelligence (SIGINT) is the act and field of intelligence-gathering by interception of signals, whether communications between people or from electronic signals not directly used in communication. Signals intelligence is a subset of intelligence collection management. As classified and sensitive information is usually encrypted, signals intelligence may necessarily involve cryptanalysis. Traffic analysis—the study of who is signaling to whom and in what quantity—is also used to integrate information, and it may complement cryptanalysis.