Polygraph in the 1940s: Post-War Boom & OSS Spy Testing

A Small Profession at the Brink of Transformation

By 1940, the polygraph was still a relatively obscure instrument used primarily by a handful of law enforcement agencies and a small cadre of trained examiners. The profession was concentrated around a few key centres: Leonarde Keeler's operation at Northwestern University's Scientific Crime Detection Laboratory (SCDL) in Chicago, a scattering of police departments in major cities, and the occasional private examiner offering services on a case-by-case basis.

The SCDL had been established in 1929 at Northwestern University, making it America's first independent forensic crime laboratory [1]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms SCDL established 1929 at Northwestern, Keeler headed polygraph department, Inbau took over directorship in 1938. Its mission encompassed toxicology, firearms identification, polygraph testing, and analysis of questioned documents [1]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms SCDL established 1929 at Northwestern, Keeler headed polygraph department, Inbau took over directorship in 1938. Leonarde Keeler headed the SCDL's polygraph department and became head of the laboratory itself in 1936 [2]Verified Leonarde Keeler - Wikipedia
Confirms Keeler born 1903, died September 20, 1949, moved to Chicago 1930, headed SCDL 1936-1938, appeared in Call Northside 777. He held that position until 1938 when he entered private business [2]Verified Leonarde Keeler - Wikipedia
Confirms Keeler born 1903, died September 20, 1949, moved to Chicago 1930, headed SCDL 1936-1938, appeared in Call Northside 777.

Keeler's portable, multi-channel instrument — the Keeler Polygraph — was the field standard, recording blood pressure, pulse, respiration, and after the 1938 addition of the psychogalvanometer, galvanic skin response (GSR) [3]Verified Leonarde Keeler — Grokipedia
Confirms Keeler's GSR addition in 1938, 1939 patent, founding of Keeler Polygraph Institute, recognised as father of modern polygraph by APA. His 1939 patent established the prototype for mass-produced instruments [3]Verified Leonarde Keeler — Grokipedia
Confirms Keeler's GSR addition in 1938, 1939 patent, founding of Keeler Polygraph Institute, recognised as father of modern polygraph by APA. The instrument was encased in a metal toolbox, making it suitable for field deployment — a crucial advantage that would prove essential during the war years [4]Verified OSS Wartime Polygraph: Spy Testing in World War II
Confirms OSS adopted polygraph circa 1943, Fort Wetherill screening of 294 POWs, Keeler Polygraph as primary WWII-era instrument, CIA Office of Security 1949 estimate.

The Legal Landscape Before the War

The legal framework for polygraph evidence was constrained. The 1923 Frye v. United States decision had effectively barred polygraph results from courtroom testimony, ruling that the technique had not gained general acceptance in the relevant scientific community [5]Verified To Tell the Truth: A Short History of the Polygraph
Confirms the 1923 Frye v. United States decision, 20,000 polygraph exams in 1963, and Employee Polygraph Protection Act of 1988. However, on February 2, 1935, Keeler had achieved a milestone when his polygraph was used in court in Portage, Wisconsin, contributing to the conviction of two assailants — the first courtroom use of polygraph evidence in securing a conviction [2]Verified Leonarde Keeler - Wikipedia
Confirms Keeler born 1903, died September 20, 1949, moved to Chicago 1930, headed SCDL 1936-1938, appeared in Call Northside 777.

John Larson's pioneering polygraph of the early 1920s, while innovative as the first instrument to continuously record multiple physiological channels simultaneously, had been bulky and cumbersome, requiring smoked drums and half an hour to set up [6]Verified Leonarde Keeler and his Instruments
Confirms Keeler's portable polygraph design, work with Larson at Berkeley PD, and instrument requiring half hour setup. Keeler's improvements — adding inked pens for recording in 1925 and creating a truly portable device — had transformed the polygraph from a laboratory curiosity into a practical field instrument [7]Verified History of Polygraph - Ohio Polygraph Services
Confirms Keeler's 1925 ink-pen improvement, 1938 GSR addition, Reid's 1947 CQT development, and 1948 founding of Keeler Polygraph Institute. Learn more about how Larson's work at the Berkeley Crime Detection Lab laid the foundation for the modern polygraph.

Birth of Intelligence Community Polygraph Testing

The Office of Strategic Services was established on June 13, 1942, by a Presidential military order issued by President Franklin D. Roosevelt [8]Verified The Office of Strategic Services — National Archives
Confirms OSS established June 13, 1942 from COI, operated in Europe/Asia/North Africa, CIA created July 26, 1947. Under the command of Major General William J. Donovan, the OSS was tasked with collecting and analysing strategic information and conducting special operations [9]Verified Office of Strategic Services Established — DVIDS
Confirms OSS employed more than 13,000 men and women, 65% Army/Army Air Force personnel. At its peak, the OSS employed nearly 13,000 men and women, approximately 65 percent of whom were U.S. Army and Army Air Force personnel [10]Verified The Office of Strategic Services: America's First Intelligence Agency — CIA
Confirms OSS employed nearly 13,000 at peak, CIA derives significant institutional legacy from OSS, key personnel and files transferred.

The OSS incorporated polygraph testing beginning around 1943 for agent screening, counterintelligence interrogations, and internal security purposes [4]Verified OSS Wartime Polygraph: Spy Testing in World War II
Confirms OSS adopted polygraph circa 1943, Fort Wetherill screening of 294 POWs, Keeler Polygraph as primary WWII-era instrument, CIA Office of Security 1949 estimate. This represented the first systematic use of lie detection technology in American intelligence operations [4]Verified OSS Wartime Polygraph: Spy Testing in World War II
Confirms OSS adopted polygraph circa 1943, Fort Wetherill screening of 294 POWs, Keeler Polygraph as primary WWII-era instrument, CIA Office of Security 1949 estimate. The primary instrument available during the WWII era was the Keeler Polygraph, which by 1942 measured three physiological channels: cardiovascular activity, respiratory patterns, and galvanic skin response [4]Verified OSS Wartime Polygraph: Spy Testing in World War II
Confirms OSS adopted polygraph circa 1943, Fort Wetherill screening of 294 POWs, Keeler Polygraph as primary WWII-era instrument, CIA Office of Security 1949 estimate.

The polygraph was introduced into federal service in the 1940s and was used in noteworthy events including investigative support for the Nuremberg Trials, counterintelligence support to the new atomic weapons facilities, and investigations of crimes in prisoner-of-war camps [11]Verified Issues Surrounding the Use of Polygraphs — U.S. Senate Hearing
Confirms polygraph introduced into federal service in the 1940s, used for Nuremberg Trials support, atomic weapons facility screening, and POW camp investigations.

Agent Screening and Counterintelligence Operations

One of the most critical applications of polygraph testing within the OSS was screening agents before deployment to enemy-occupied territory. The consequences of sending an untrustworthy agent into the field were catastrophic: compromised networks, captured operatives, blown operations, and lost lives [4]Verified OSS Wartime Polygraph: Spy Testing in World War II
Confirms OSS adopted polygraph circa 1943, Fort Wetherill screening of 294 POWs, Keeler Polygraph as primary WWII-era instrument, CIA Office of Security 1949 estimate.

The OSS recruited from extraordinarily diverse backgrounds. In Europe, operatives were drawn from refugee communities, resistance movements, and even captured enemy prisoners willing to work against their former masters. In Asia, the OSS worked with Chinese, Thai, Vietnamese, and other nationals — notably through Detachment 101 in Burma, one of the most successful unconventional warfare operations of WWII [4]Verified OSS Wartime Polygraph: Spy Testing in World War II
Confirms OSS adopted polygraph circa 1943, Fort Wetherill screening of 294 POWs, Keeler Polygraph as primary WWII-era instrument, CIA Office of Security 1949 estimate.

The X-2 counterespionage branch employed polygraph testing in particularly high-stakes situations involving suspected enemy agents, captured operatives, and individuals whose loyalty was in doubt [4]Verified OSS Wartime Polygraph: Spy Testing in World War II
Confirms OSS adopted polygraph circa 1943, Fort Wetherill screening of 294 POWs, Keeler Polygraph as primary WWII-era instrument, CIA Office of Security 1949 estimate. Running successful double-agent operations required confidence that "turned" agents were genuinely cooperating, and the polygraph became an important tool in this evaluation process.

At Fort Wetherill in August 1945, 294 German POWs were screened, with 47% rejected based on polygraph and other criteria — documenting one of the programme's largest confirmed operations [4]Verified OSS Wartime Polygraph: Spy Testing in World War II
Confirms OSS adopted polygraph circa 1943, Fort Wetherill screening of 294 POWs, Keeler Polygraph as primary WWII-era instrument, CIA Office of Security 1949 estimate. German POWs at these Rhode Island facilities took polygraph tests supervised by police officials from major American cities, and those with Nazi sympathies, communist leanings, or insincere motives were identified and removed [12]Verified POW Camps at Forts Getty and Wetherill — Rhode Island History
Confirms German POWs at Fort Wetherill took polygraph tests supervised by police officials, those with Nazi sympathies were removed.

The Man Behind the Instrument

Leonarde Keeler (October 30, 1903 – September 20, 1949) was the central figure in polygraph development throughout the 1940s [2]Verified Leonarde Keeler - Wikipedia
Confirms Keeler born 1903, died September 20, 1949, moved to Chicago 1930, headed SCDL 1936-1938, appeared in Call Northside 777. Born in North Berkeley, California, Keeler had been captivated as a high school student by John Larson's "cardio-pneumo psychogram" and dedicated his life to developing the modern polygraph [2]Verified Leonarde Keeler - Wikipedia
Confirms Keeler born 1903, died September 20, 1949, moved to Chicago 1930, headed SCDL 1936-1938, appeared in Call Northside 777. He was recognised by the American Polygraph Association as the "father of the modern polygraph" [3]Verified Leonarde Keeler — Grokipedia
Confirms Keeler's GSR addition in 1938, 1939 patent, founding of Keeler Polygraph Institute, recognised as father of modern polygraph by APA.

By 1940, records in Keeler's office covered more than 30,000 cases, which showed a high percentage of accuracy and successful results [13]Verified Baltimore Police Museum — Polygraph History
Confirms Keeler over 30,000 cases, opened first polygraph school, worked as private consultant until death 1949. His Keeler Polygraph had become the undisputed standard for both law enforcement and the emerging military applications of lie detection.

During the war, Keeler's instruments were deployed in military and intelligence settings. Leonard Harrelson reported that a specific Keeler Polygraph device was used by Keeler himself in 1944 to examine German POWs at Fort Getty, Rhode Island, to determine their suitability to become police officers in post-WWII Germany [14]Verified Leonard Keeler — The Father of the Modern Polygraph
Confirms Keeler used polygraph in 1944 at Fort Getty on German POWs, Associated Research Inc manufactured Keeler Polygraphs. This wartime application demonstrated the polygraph's potential as a mass personnel screening tool.

Film, Fame, and the Popularisation of Polygraph

Keeler's public profile extended beyond the laboratory. In 1948, he appeared as himself in the film noir docudrama Call Northside 777, alongside James Stewart, Richard Conte, and Lee J. Cobb [2]Verified Leonarde Keeler - Wikipedia
Confirms Keeler born 1903, died September 20, 1949, moved to Chicago 1930, headed SCDL 1936-1938, appeared in Call Northside 777. Keeler insisted on playing the examiner because he was certain that no actor could learn to use the machine properly [15]Verified Leonarde Keeler — IMDb Biography
Confirms Keeler insisted on playing the examiner in Call Northside 777 because no actor could learn the machine.

Keeler's high-profile examinations throughout the 1940s brought widespread public awareness to the polygraph. His role in testing suspect Dr. Frank Sweeney in the Ohio Cleveland Torso Murders case, working closely with famed detective Eliot Ness, had already cemented his reputation in the previous decade [16]Verified Keeler, Leonard — Encyclopedia.com
Confirms Keeler's GSR addition, 1948 founding of first polygraph school, role in forensic science and Cleveland Torso Murders case. By the 1940s, Keeler was the nation's foremost polygraph authority.

Tragically, Keeler's personal life was marked by hardship. His wife Katherine, a pioneering female handwriting analyst, left him and died in 1944 while flying as a WASP (Women's Auxiliary Service Pilot) [2]Verified Leonarde Keeler - Wikipedia
Confirms Keeler born 1903, died September 20, 1949, moved to Chicago 1930, headed SCDL 1936-1938, appeared in Call Northside 777. Devastated by this loss, Keeler died in 1949 in Door County, Wisconsin, at the age of 45, after suffering a stroke brought on by stress, alcohol, and cigarettes [2]Verified Leonarde Keeler - Wikipedia
Confirms Keeler born 1903, died September 20, 1949, moved to Chicago 1930, headed SCDL 1936-1938, appeared in Call Northside 777. Since his death, as noted in the Polygraph journal, "no one in the polygraph field has taken Leonarde Keeler's place" [17]Verified Biography of Leonarde Keeler
Confirms since Keeler's death in 1949, no one in the polygraph field has taken his place.

The Fundamental Shift in Polygraph Application

Perhaps the most consequential development of the 1940s was the transformation of the polygraph from a criminal investigation tool into a mass personnel screening device. Before the war, polygraph examinations were conducted primarily on criminal suspects — individuals already under suspicion for specific offences. The wartime experience of screening entire populations of recruits, agents, and military personnel fundamentally altered the profession's trajectory.

In the 1940s, polygraph use expanded significantly to the private sector, particularly for screening job applicants in industries such as defence, security, and law enforcement [18]Verified Polygraph Examinations for Employment in the US
Confirms 1940s expansion of polygraph to private sector for job applicant screening in defence, security, and law enforcement. The rationale was that individuals with something to hide would be deterred from applying, and those who did apply could be subjected to a polygraph test as a condition of employment [18]Verified Polygraph Examinations for Employment in the US
Confirms 1940s expansion of polygraph to private sector for job applicant screening in defence, security, and law enforcement.

Keeler himself had pioneered commercial employee screening as early as 1931 when he first implemented the Relevant-Irrelevant (RI) technique for employee screening at banks [19]Verified Chicago: Birthplace of Modern Polygraphy
Confirms Keeler first implemented RI technique in 1931 for employee screening at banks. By the late 1940s, this practice had expanded enormously, with major retailers, banks, and manufacturers hiring polygraph examiners to screen employees for theft and dishonesty. For more on the development of the history of the Relevant-Irrelevant test, see our dedicated guide.

The Post-War Private Examiner Boom

The end of World War II created a massive talent pool of military-trained interrogators and deception detection specialists. Hundreds of these professionals entered the private sector after the war, creating the modern polygraph industry virtually overnight. The private polygraph business model — offering employee screening, theft investigations, and pre-employment testing to corporations — became a rapidly growing sector of the American economy.

The Keeler Polygraph Model 6317, developed during this era, was specifically designed for the booming field of employment screening and was later utilised by the CIA during the Korean War [20]Verified Baltimore Police Museum — Keeler Model 6317
Confirms Keeler Model 6317 was designed for employment screening, later used by CIA during Korean War. This proliferation of both instruments and trained examiners meant that by the end of the decade, polygraph testing had become an accepted part of corporate America's personnel management toolkit.

The Most Important Methodological Innovation

John E. Reid, a Chicago lawyer and polygraph expert, developed the Control Question Technique (CQT) in 1947 — what many regard as the single most important methodological innovation in polygraph history [21]Verified History of Polygraph — 90210 Polygraph
Confirms Reid developed CQT between 1945 and 1947, Keeler founded world's first polygraph school in 1948. Reid was a member of the staff at the Chicago Police Scientific Crime Detection Laboratory and had extensive experience in lie-detection examination of criminal suspects [22]Verified The Polygraph Technique, Part I: Theory — John E. Reid & Associates
Confirms in the 1940s John E. Reid developed the Control Question polygraph technique.

In 1947, Reid published a paper in the Journal of Criminal Law and Criminology in which he introduced two types of control questions — a "guilt complex" question and a "comparative response" question [23]Verified Control Question — Polygraph UK Glossary
Confirms in 1947 Reid published paper introducing guilt complex and comparative response control questions. The CQT incorporated control questions designed to be emotionally arousing for non-deceptive subjects and less emotionally arousing for deceptive subjects than the relevant questions previously used [21]Verified History of Polygraph — 90210 Polygraph
Confirms Reid developed CQT between 1945 and 1947, Keeler founded world's first polygraph school in 1948.

Reid's CQT replaced the Relevant/Irrelevant Question Technique (RIT), which used only relevant or irrelevant questions during examinations [21]Verified History of Polygraph — 90210 Polygraph
Confirms Reid developed CQT between 1945 and 1947, Keeler founded world's first polygraph school in 1948. Since its inception in the late 1940s, the CQT has remained the most widely used polygraph test [24]Verified A Review of the Polygraph: History, Methodology and Current Status
Confirms CQT remains the most widely used polygraph test since its inception by Reid in the late 1940s. Reid had earlier made another contribution in 1945 when he developed a device that recorded muscular activity accompanying changes in blood pressure, claiming greater accuracy when these recordings were made simultaneously with standard measurements [25]Verified Polygraph — Wikipedia
Confirms Reid's 1945 device recording muscular activity with blood pressure, Keeler's GSR addition in 1939, FBI prototype. You can learn more about requesting a specific polygraph technique in our comprehensive guide.

Reid's Professional Legacy

Reid met Fred E. Inbau when he joined the Scientific Crime Detection Laboratory in 1940 [26]Verified Fred E. Inbau — Social Networks and Archival Context
Confirms Inbau-Reid collaboration, Reid joining SCDL in 1940, Reid forming agency in 1947, joint publications. This partnership would prove remarkably productive for the field of deception detection. Reid formed his own detective agency, John E. Reid and Associates, in 1947 [26]Verified Fred E. Inbau — Social Networks and Archival Context
Confirms Inbau-Reid collaboration, Reid joining SCDL in 1940, Reid forming agency in 1947, joint publications, establishing one of the most enduring organisations in the polygraph profession.

Reid's approach to polygraph methodology represented a sophisticated understanding of human psychology. He theorised that a subject would exhibit the most significant arousal to questions holding the greatest emotional weight [22]Verified The Polygraph Technique, Part I: Theory — John E. Reid & Associates
Confirms in the 1940s John E. Reid developed the Control Question polygraph technique. This insight — that comparison between different types of questions could reveal deception more reliably than simple question-and-answer formats — revolutionised the field.

Reid continued his work until his death in 1982 [26]Verified Fred E. Inbau — Social Networks and Archival Context
Confirms Inbau-Reid collaboration, Reid joining SCDL in 1940, Reid forming agency in 1947, joint publications, by which time his techniques had become the dominant approach in both law enforcement and private sector polygraph testing. His collaboration with Inbau produced several influential publications including Truth and Deception: The Polygraph Technique [26]Verified Fred E. Inbau — Social Networks and Archival Context
Confirms Inbau-Reid collaboration, Reid joining SCDL in 1940, Reid forming agency in 1947, joint publications.

Fred E. Inbau: Legal Scholar and Polygraph Advocate

Fred E. Inbau (1909–1998) was a Northwestern University legal scholar who provided crucial academic and legal legitimacy to the polygraph field [27]Verified Fred E. Inbau Papers Finding Aid — Northwestern University
Confirms Inbau's career at Northwestern: first published book 1942, extensive publications, founded AELE. Inbau's first position at Northwestern in 1933 was as a research assistant in the SCDL [28]Verified Fred E. Inbau Papers — Guide
Confirms Inbau first position at Northwestern 1933, SCDL Director 1938, law professor 1945. He was named Director of the SCDL in 1938 when it was sold by Northwestern to the Chicago Police Department [28]Verified Fred E. Inbau Papers — Guide
Confirms Inbau first position at Northwestern 1933, SCDL Director 1938, law professor 1945.

After leaving the SCDL, Inbau served in private practice as a trial attorney until 1945, when he returned to Northwestern University as a professor of law [28]Verified Fred E. Inbau Papers — Guide
Confirms Inbau first position at Northwestern 1933, SCDL Director 1938, law professor 1945. His first book, Lie Detection and Criminal Interrogation (1942), became a foundational text in the field [29]Verified Fred Inbau — AELE Biography
Confirms Inbau joined SCDL staff 1933, became first director when Chicago PD took over 1938, joined NU law faculty 1945. For the third edition in 1953, Inbau invited John Reid as co-author for a new section on lie detector techniques, including the control question [30]Verified Reid Technique — Wikipedia
Confirms Inbau's 1942 book, Reid co-author for 1953 edition, both Keeler and Reid set up polygraph training clinics in Chicago.

Inbau's extensive publications included over fifty journal articles and eighteen books in criminal law and scientific investigation [27]Verified Fred E. Inbau Papers Finding Aid — Northwestern University
Confirms Inbau's career at Northwestern: first published book 1942, extensive publications, founded AELE. Like his mentor, John H. Wigmore, Inbau believed that scientific methods were essential to abolishing "cruel and ineffective methods of establishing criminal identity" [27]Verified Fred E. Inbau Papers Finding Aid — Northwestern University
Confirms Inbau's career at Northwestern: first published book 1942, extensive publications, founded AELE. Read our complete profile of Fred Inbau and the polygraph for more on his remarkable contributions.

Cleve Backster: From CIA to Polygraph Pioneer

Grover Cleveland "Cleve" Backster Jr. (February 27, 1924 – June 24, 2013) was one of the most significant polygraph figures to emerge from the 1940s military-intelligence pipeline [31]Verified Cleve Backster — Wikipedia
Confirms Backster as CIA interrogation specialist who founded CIA's polygraph unit after WWII. In January 1943, Backster enlisted in the Navy and was honourably released in July 1946, receiving a World War II Victory Medal [32]Verified Cleve Backster Papers — University of West Georgia
Confirms Backster's Navy service WWII, Army CIC enlistment March 1947, CIA employment 1948, founding CIA polygraph programme 1949.

In March 1947, Backster re-enlisted with the Army Counter Intelligence Corps, where he became involved in criminal investigation and counterintelligence techniques at Fort Holabird, Maryland [32]Verified Cleve Backster Papers — University of West Georgia
Confirms Backster's Navy service WWII, Army CIC enlistment March 1947, CIA employment 1948, founding CIA polygraph programme 1949. He was honourably discharged in April 1948, whereupon he joined the CIA in Washington, DC, and became an interrogation specialist [32]Verified Cleve Backster Papers — University of West Georgia
Confirms Backster's Navy service WWII, Army CIC enlistment March 1947, CIA employment 1948, founding CIA polygraph programme 1949. In 1949, he instituted the CIA's polygraph examination program [32]Verified Cleve Backster Papers — University of West Georgia
Confirms Backster's Navy service WWII, Army CIC enlistment March 1947, CIA employment 1948, founding CIA polygraph programme 1949.

Backster received training from Leonarde Keeler himself and later became director of the Keeler Polygraph Institute in Chicago after Keeler's death [33]Verified Cleve Backster — Psi Encyclopedia
Confirms Backster received training from Keeler, became director of Keeler Polygraph Institute after Keeler's death, developed Zone Comparison Technique. He went on to develop the Backster Zone Comparison Technique, the first polygraph interpretation system to use a numerical evaluation — a system still much in use today [33]Verified Cleve Backster — Psi Encyclopedia
Confirms Backster received training from Keeler, became director of Keeler Polygraph Institute after Keeler's death, developed Zone Comparison Technique. Discover more about Backster's extraordinary career in our profile of Cleve Backster: Polygraph Pioneer.

The CIA and the National Security Act of 1947

The CIA was created under the National Security Act of 1947, which President Truman signed on July 26, 1947 [34]Verified Ask Molly: The National Security Act of 1947 — CIA
Confirms CIA created under National Security Act signed July 26, 1947, officially came into existence September 18, 1947. The CIA officially came into existence on September 18 of that same year [34]Verified Ask Molly: The National Security Act of 1947 — CIA
Confirms CIA created under National Security Act signed July 26, 1947, officially came into existence September 18, 1947. When the CIA replaced the OSS, it absorbed personnel, methods, and institutional lessons that directly shaped the most extensive polygraph programme in intelligence history [4]Verified OSS Wartime Polygraph: Spy Testing in World War II
Confirms OSS adopted polygraph circa 1943, Fort Wetherill screening of 294 POWs, Keeler Polygraph as primary WWII-era instrument, CIA Office of Security 1949 estimate.

According to CIA records, one-third of the new agency's employees were former OSS [35]Verified Secret Agents, Secret Armies: The Short Happy Life of the OSS
Confirms one-third of CIA's employees were former OSS, four directors were former OSS officers. Today's Central Intelligence Agency derives a significant institutional and spiritual legacy from the OSS — key personnel, files, funds, procedures, and contacts assembled by the OSS found their way into the CIA more or less intact [36]Verified The Office of Strategic Services: America's First Intelligence Agency — CIA Museum
Confirms CIA derives significant institutional and spiritual legacy from OSS, key personnel and files transferred intact. Four future Directors of Central Intelligence — Allen Dulles, Richard Helms, William Colby, and William Casey — served in the OSS [35]Verified Secret Agents, Secret Armies: The Short Happy Life of the OSS
Confirms one-third of CIA's employees were former OSS, four directors were former OSS officers.

The CIA Office of Security estimated in 1949 that polygraph testing worked successfully on seven out of eight cases, providing early validation that supported the programme's expansion [4]Verified OSS Wartime Polygraph: Spy Testing in World War II
Confirms OSS adopted polygraph circa 1943, Fort Wetherill screening of 294 POWs, Keeler Polygraph as primary WWII-era instrument, CIA Office of Security 1949 estimate. This favourable assessment helped establish the polygraph as a permanent fixture of intelligence community security screening. For a deeper look at how the CIA's programme evolved, see our CIA Polygraph Exam: Complete Candidate Guide.

Soviet Espionage and the Demand for Screening

The late 1940s saw a series of devastating espionage revelations that dramatically accelerated the adoption of polygraph screening across U.S. intelligence agencies. Klaus Fuchs was arrested on February 2, 1950, and charged with violations of the Official Secrets Act for passing atomic bomb secrets to the Soviet Union [37]Verified Klaus Fuchs — Wikipedia
Confirms Fuchs arrested February 2, 1950, charged with violations of Official Secrets Act, confessed January 1950. His testimony to British and American intelligence agencies eventually led to the arrests of Harry Gold, David Greenglass, and Julius and Ethel Rosenberg [38]Verified Klaus Fuchs — Atomic Heritage Foundation
Confirms Fuchs testimony led to arrests of Harry Gold, David Greenglass, and Julius and Ethel Rosenberg.

Fuchs had been working at the Los Alamos Laboratory during the Manhattan Project, where he was responsible for many significant theoretical calculations relating to nuclear weapons [37]Verified Klaus Fuchs — Wikipedia
Confirms Fuchs arrested February 2, 1950, charged with violations of Official Secrets Act, confessed January 1950. His espionage is credited with enabling the Soviets to develop their atomic bomb one to two years earlier than otherwise expected [39]Verified Klaus Fuchs — Britannica
Confirms Fuchs espionage credited with saving Soviets at least one year in atomic bomb development. Decrypted cables from the VENONA project had revealed Fuchs as a Soviet spy as early as 1949 [38]Verified Klaus Fuchs — Atomic Heritage Foundation
Confirms Fuchs testimony led to arrests of Harry Gold, David Greenglass, and Julius and Ethel Rosenberg.

These espionage discoveries sent shockwaves through the intelligence community and intensified demands for more rigorous security screening measures. The polygraph was seen as a practical tool for vetting the thousands of personnel who had access to classified information. Understanding the evolution of security screening helps explain why agencies like the ATF require polygraph tests as part of their hiring process today.

The World's First Polygraph School

In 1948, Leonarde Keeler founded the world's first polygraph school — the Keeler Polygraph Institute — in Chicago, Illinois [40]Verified A Comprehensive History of the Polygraph — Polygraph UK
Confirms Keeler opened world's first polygraph school in Chicago, formalised professional training standards. This establishment formalised polygraph training and marked the profession's transition from an experimental technique to an established practice requiring specialised education [41]Verified Polygraph Machine Used on Jack Ruby — FBI
Confirms FBI employing polygraph examinations since early days of FBI Laboratory, expanded use around WWII.

The school instructed students on how to conduct and analyse the results of polygraph examinations [16]Verified Keeler, Leonard — Encyclopedia.com
Confirms Keeler's GSR addition, 1948 founding of first polygraph school, role in forensic science and Cleveland Torso Murders case, formalising what had previously been an apprenticeship-style training system. Before the Keeler Institute, aspiring polygraph examiners learned through informal mentorship — spending time alongside experienced practitioners and gradually developing their skills through observation and supervised practice.

The establishment of formal training standards was essential for the profession's growth. As polygraph testing expanded from a few dozen practitioners into a nationwide industry, consistent methodology and quality control became critical. The Keeler Polygraph Institute set benchmarks that would influence polygraph education for decades. After Keeler's death in 1949, Cleve Backster became director of the Institute [33]Verified Cleve Backster — Psi Encyclopedia
Confirms Backster received training from Keeler, became director of Keeler Polygraph Institute after Keeler's death, developed Zone Comparison Technique, ensuring continuity of Keeler's teaching legacy. Today, professional polygraph training continues to build on the foundations Keeler established.

Instrument Technology Advances

The 1940s saw significant advances in polygraph instrument design. Keeler's Model #301, the first polygraph manufactured for him by Associated Research, Inc. of Chicago, Illinois, served as the standard instrument through the decade [14]Verified Leonard Keeler — The Father of the Modern Polygraph
Confirms Keeler used polygraph in 1944 at Fort Getty on German POWs, Associated Research Inc manufactured Keeler Polygraphs. The device recorded multiple channels of physiological data simultaneously, using ink pens on a moving chart — a vast improvement over John Larson's original smoked-drum apparatus [7]Verified History of Polygraph - Ohio Polygraph Services
Confirms Keeler's 1925 ink-pen improvement, 1938 GSR addition, Reid's 1947 CQT development, and 1948 founding of Keeler Polygraph Institute.

A device recording muscular activity accompanying changes in blood pressure was developed in 1945 by John E. Reid, who claimed that greater accuracy could be obtained by making these recordings simultaneously with standard measurements [25]Verified Polygraph — Wikipedia
Confirms Reid's 1945 device recording muscular activity with blood pressure, Keeler's GSR addition in 1939, FBI prototype. This represented an important expansion of the physiological channels being monitored.

The Keeler instruments were built for portability and field reliability — essential qualities for wartime deployment. The devices were housed in custom-built steel cases manufactured by the Kennedy Tool Box company, featuring a brown wrinkle-finish paint scheme [14]Verified Leonard Keeler — The Father of the Modern Polygraph
Confirms Keeler used polygraph in 1944 at Fort Getty on German POWs, Associated Research Inc manufactured Keeler Polygraphs. These rugged instruments could be transported to POW camps, military bases, and intelligence field offices around the world. To understand more about the physiological responses measured during polygraph testing, see our detailed scientific guide.

The FBI's Cautious Approach

While the OSS embraced polygraph testing enthusiastically, J. Edgar Hoover and the FBI took a more measured approach. The FBI has been employing polygraph examinations since the early days of the FBI Laboratory, and around World War II, the FBI began using polygraphs in the course of investigations to confirm facts and dispel lies [42]Verified To Tell the Truth: A Short History of the Polygraph — Library of Congress
Confirms approximately one million polygraph examinations annually for employment between 1981-1988 before EPPA.

The FBI's position reflected a careful institutional philosophy. Rather than adopting polygraph wholesale as a screening tool, the Bureau integrated it selectively into investigative work. This cautious but pragmatic approach would continue to characterise the FBI's relationship with polygraph testing for decades. For more on this fascinating tension, read our article on J. Edgar Hoover and the FBI's early scepticism of polygraphs.

Despite Hoover's reservations, the wartime period demonstrated that polygraph testing had genuine utility in intelligence and security contexts. The FBI's use of polygraph during this era, even if more limited than the OSS's, helped establish precedents that would eventually expand significantly in the Cold War years.

A Decade That Defined the Modern Polygraph Profession

The 1940s established virtually every foundation upon which modern polygraph practice rests. The decade's achievements include the transformation of polygraph from criminal investigation to personnel screening, the creation of the first formal training institution, the development of the Control Question Technique that remains dominant today, and the embedding of polygraph testing into the permanent architecture of American intelligence and national security.

The OSS wartime polygraph programme proved that lie detection could serve intelligence operations at scale, establishing a precedent that influenced every major Western intelligence agency [4]Verified OSS Wartime Polygraph: Spy Testing in World War II
Confirms OSS adopted polygraph circa 1943, Fort Wetherill screening of 294 POWs, Keeler Polygraph as primary WWII-era instrument, CIA Office of Security 1949 estimate. When the CIA absorbed the OSS legacy, it created a continuous institutional commitment to polygraph screening that persists to the present day. The U.S. government now has 24 polygraph programmes, staffed with approximately 500 polygraph examiners serving in all regions of the country and much of the world [11]Verified Issues Surrounding the Use of Polygraphs — U.S. Senate Hearing
Confirms polygraph introduced into federal service in the 1940s, used for Nuremberg Trials support, atomic weapons facility screening, and POW camp investigations.

The post-war boom in private polygraph testing — fuelled by returning military specialists and growing corporate demand — created an industry that would transform employment practices across America. By the time the Employee Polygraph Protection Act regulated private-sector testing in 1988, approximately one million polygraph examinations were being conducted annually for employment purposes. The foundations for this extraordinary expansion were laid in the 1940s.

The decade also saw the profession begin to take institutional shape. From the SCDL in Chicago to the Keeler Polygraph Institute, the 1940s created the educational infrastructure, methodological frameworks, and professional networks that would sustain the field through the Cold War and into the modern era. Understanding how the polygraph evolved through this period is essential context for anyone interested in how software later changed the lie detector test in the digital age.