Stimson Closes Yardley's Black Chamber, Briefly Interrupting U.S. Peacetime Signals Intelligence

Opening

Secretary of State Henry L. Stimson formally withdraws State Department funding from the Black Chamber — the joint State-War cryptanalytic bureau operated by Herbert O. Yardley since 1919 — on October 31, 1929, effectively terminating it. Stimson’s widely-cited (and perhaps apocryphal) justification, delivered privately to colleagues years later, was that “gentlemen do not read each other’s mail.” The Black Chamber had produced partial decryption of Japanese diplomatic traffic during the 1921-1922 Washington Naval Conference, intercepts that had given U.S. negotiators decisive knowledge of Japanese positions. Stimson’s closure creates a brief peacetime-SIGINT interruption but the capability quickly resurfaces — Army Signal Intelligence Service stands up 1930, operating continuously thereafter and becoming the institutional ancestor of the 1952-11-04–nsa-founded-by-classified-directive.

What Happened / Key Facts

The Black Chamber’s 1919-1929 operation:

• Founded 1919: MI-8 (Army Military Intelligence) Cipher Bureau combined with State Department Code and Cipher Bureau under the civilian name “Cipher Bureau” — Yardley’s internal name was “Black Chamber” or “American Black Chamber.”
• Headquarters: New York City (rather than Washington, to preserve plausible deniability).
• Staff: Approximately 25 cryptanalysts and linguists.
• Major success: Decryption of Japanese diplomatic communications enabling U.S. to know Japanese delegation’s minimum acceptable naval-tonnage ratios during the 1921-1922 Washington Naval Conference.
• Funding structure: Joint State-War Department funding, routed through State’s Code and Cipher Bureau to preserve budgetary invisibility.

Stimson’s closure decision:

• Stimson becomes Secretary of State: March 28, 1929, Hoover administration.
• Briefing on Black Chamber: May 1929 (sources vary on exact date). Stimson reviews decrypted Japanese cables including personal communications and diplomatic instructions.
• Decision: Stimson orders State Department funding withdrawn. The “gentlemen do not read each other’s mail” comment appears in his 1948 memoir On Active Service in Peace and War (coauthor McGeorge Bundy) describing Stimson’s recollection of his 1929 reasoning.
• Continuation with Army funding: Though State withdrew, Army Signal Corps cryptanalytic work continued under William F. Friedman’s Signal Intelligence Service (created April 1930). Friedman’s operation was smaller and less capable than Yardley’s but provided continuity.

Yardley’s aftermath:

• 1931: Yardley publishes The American Black Chamber, revealing U.S. cryptanalytic operations and specifically the Japanese-cable decryption. Publication was legal (no espionage statute then covered his disclosure of his own prior work) but caused substantial diplomatic damage.
• 1933: Congress passes the “Yardley Act” (18 U.S.C. § 798) specifically to criminalize disclosure of classified communications intelligence.
• Later career: Yardley worked briefly for Chinese Nationalist cryptanalytic services in 1938-1940; was denied return to U.S. government service during WWII despite his expertise; died in obscurity 1958.

Why This Event Matters

The Black Chamber episode is a rare case where a U.S. administration explicitly chose to curtail intelligence activity on ethical grounds, only to have the capability reconstituted within months:

• Ethical restraint as temporary constraint. Stimson’s 1929 decision reflects a moral-political judgment that peacetime signals intelligence against nominally friendly nations was inconsistent with diplomatic conduct. The judgment was personal and institutional, not driven by external disclosure or scandal. Within a decade (WWII mobilization) and certainly by 1952 (NSA founding) the judgment was reversed — not by explicit decision, but by incremental expansion of peacetime SIGINT operations under military cover.
• Institutional persistence despite executive action. The Friedman-led Signal Intelligence Service preserved cryptanalytic capability through the 1930s even without Black Chamber’s specific mission authorization. When WWII mobilization permitted expansion, the foundational capacity was available. The pattern — intelligence capability survives administrative curtailment because its institutional home preserves the tradecraft — recurs throughout U.S. intelligence history. Church Committee’s 1975 reforms, for example, did not actually eliminate capabilities Hoover had built; they renamed and relocated them.
• Stimson’s reputation vs. operational effect. Stimson is recurrently invoked by civil-liberties advocates as the model of an intelligence-constraining public servant. The operational reality is that Stimson’s decision interrupted SIGINT for approximately six months before resuming. The larger point — the near-impossibility of genuinely curtailing intelligence operations once institutionalized — deserves more attention than the individual decision.

Broader Context

Stimson himself returned to government as FDR’s Secretary of War (July 1940-September 1945) and presided over massive wartime SIGINT expansion including the VENONA predecessor operations and the Arlington Hall Station cryptanalytic center. The 1929 “gentlemen do not read mail” formulation was not applied to wartime SIGINT in any form. Stimson explicitly authorized expanded Army and Navy signals intelligence operations against both Axis powers and neutral communications. The rhetorical framing of the 1929 decision turned out to describe personal preference in peacetime, not institutional or legal constraint.

Research Gaps

• Yardley’s specific 1929 Japanese-cable decrypts partially declassified; full content at NARA RG 457

Related Entries

• 1917-01-16–zimmermann-telegram-intercepted
• 1943-02-01–venona-project-army-cryptanalysis-soviet-cable
• 1952-11-04–nsa-founded-by-classified-directive