# Operation Fitzwilliam

Operation Fitzwilliam was a highly classified US Air Force operation with the objective of developing methods for Long Range Detection (LRD) of nuclear detonations. Conducted in conjunction with Operation Sandstone, the 1948 atomic tests at Eniwetok Atoll, it integrated airborne radioactive debris collection, seismic monitoring, and atmospheric acoustic wave detection to ensure that the U.S. could detect, track, and analyze nuclear detonations worldwide.

## Origins

Following World War II the U.S. held a nuclear monopoly but military and intelligence officials warned that this advantage would not last. Rising tensions with the Soviet Union, along with evidence of espionage and scientific advancements, made it clear that nuclear proliferation was inevitable. Lewis L. Strauss, of the Atomic Energy Commission (AEC) became concerned that the U.S. had no system in place for monitoring Soviet nuclear activity.
In September 1947, President Harry S. Truman initiated a directive instructing the U.S. military to develop a global system for detecting nuclear detonations. The directive was prompted by intelligence indicating that the Soviet Union was actively pursuing nuclear weapons development. In response, General Carl A. Spaatz, commanding general of the Air Forces, assigned Major General William E. Kepner, head of the Air Force Special Weapons Group and Deputy Commander of the newly formed Joint Task Force 7 (JTF-7), to lead the effort in organizing Long-Range Detection (LRD).
With the necessity for a dedicated technical unit composed of experts in physics, meteorology, chemistry, geophysics, engineering, and military operations, General Kepner established AFMSW-1 (Air Force Materiel Special Weapons-1) on December 31, 1947. Major General Albert P. Hegenberger was appointed as the military commander, while Dr. Ellis Johnson was named technical director, overseeing the recruitment and assignment of scientists from research institutions, military laboratories, and classified programs. Personnel would be selected from key projects, including Project Mogul and radiochemical analysis teams with prior experience in Manhattan Project-era research.

## Urgency and Planning Challenges

By early 1948, planning was already well underway for Operation Sandstone, the Atomic detonation tests scheduled to take place at Eniwetok Atoll in April and May 1948. Initially, no provisions had been made to incorporate nuclear detection experiments into Sandstone. It was not until January 1948 that General Kepner and his staff formally approved integrating a Long-Range Detection (LRD) component into the tests. This late decision forced the newly formed AFMSW-1 to have to develop and deploy its detection capabilities in a compressed timeframe and with many technical and logistical hurdles.

### 1. Logistical and Deployment Issues

* Operation Fitzwilliam required a vast network of airborne and ground-based stations, with aircraft operating from Hickam Field (Hawaii), Kwajalein, Guam, Alaska, California, and several other locations across the globe. Getting the necessary equipment, aircraft modifications, and trained personnel into place before the Sandstone tests proved to be a major undertaking.
* Many of the stations were in remote locations, requiring long-range transport of specialized instruments, aircraft modifications, and radiochemical laboratories. Weather conditions and supply chain delays further complicated deployment.
* The operation required radioactive sampling aircraft, but equipping B-29 bombers with airborne filter systems, modifying them for extended flights, and ensuring their availability for the mission required hurried last-minute adjustments.
* Ground stations needed to be set up in time to capture nuclear debris from the explosions, but construction, equipment installation, and testing were so rushed that there was a concern about accuracy and data reliability.

### 2. Scientific and Technical Limitations

* The nuclear detection methods being used were still experimental. The technology for high-altitude air sampling, radiochemical analysis, and fallout tracking was in its early stages, with no prior large-scale field testing before the Sandstone detonations.
* Aircraft contamination was a major concern. Planes flying through radioactive clouds risked being permanently contaminated, which would make repeated flights difficult and would require extensive decontamination procedures.
* The airborne filtering systems used to collect radioactive particles were unreliable, with the possibility of filters becoming clogged or failing to capture sufficient samples.

### 3. Coordination and Intelligence Gaps

* The successful integration of Fitzwilliam into Sandstone necessitated close coordination among multiple agencies, including the U.S. Air Force, Army, Navy, Atomic Energy Commission, and intelligence services. Fitzwilliam's objectives had to be fully aligned with those of the Sandstone tests, ensuring no interference with ongoing operations. Achieving this required full cooperation between the leadership of Joint Task Force 7 (JTF-7), responsible for Sandstone, and AFMSW-1 overseeing Fitzwilliam.
* Communication failures between different branches slowed deployment. Conflicting security protocols, limited information-sharing, and classified restrictions made coordination difficult between military planners and scientists.
* Personnel shortages were a problem, as only a small number of trained experts were available for nuclear detection. Rapid training programs were implemented, but many personnel arrived in the Pacific with minimal preparation for handling classified radiochemical materials or interpreting nuclear fallout data.
* Eniwetok AtollThe urgency of the mission meant there was no opportunity for a proper full-scale rehearsal or pre-test calibration, forcing teams to rely on incomplete field testing and last-minute troubleshooting.

## Military Leadership and Execution

To address these challenges, Major General Hegenberger appointed Brigadier General Morris R. Nelson to oversee the integration of Fitzwilliam into the broader objectives of Sandsone and Col. Herbert W. Ehrgott was tasked with procurement and deployment of necessary equipment and resources for the operation. Both men were class of 1926 West Point classmates.
Col. Benjamin G. Holzman, an Air Force meteorologist and weather specialist, would contributing to both Operation Sandstone and Fitzwilliam, providing critical insights into the dispersion of nuclear debris in the upper atmosphere and coordinating global data collection at remote test sites. Holzman had previously contributed to Project Trinity and Operation Crossroads, where he helped develop meteorological tracking models.
In late January 1948, Col. Nelson P. Jackson of Joint Task Force 7 (JTF-7) was assigned to AFMSW-1 to serve as the Operations Officer for Fitzwilliam. Reporting directly to General Kepner, he would facilitate the integration of Fitzwilliam into the existing operational and deployment framework of Sandstone. He was a former Commander of the 64th Fighter Wing during World War II, with experience in high-level military coordination. Additionally, he would be able to serve as the primary liaison between the two Operations and The Pentagon. Both Col. Alfred D. Starbird, the Deputy Chief of Staff for JTF-7, and Col. Milton F. Summerfelt, the Deputy Chief of Staff for Operations at the Atomic Energy Office were Jackson's classmates from the West Point Class of 1933 ("M" Company).

### Logistical Coordination

Col. Jackson departed Washington, D.C., on February 10, 1948, and arrived at Fort Shafter, Hawaii, on February 12. Upon arrival, he coordinated with key military units throughout February and early March 1948 to provide support for Operation Fitzwilliam:$^{:185,202,203,235}$
* Pacific Air Command – Would deploy aircraft for airborne nuclear debris collection.
* U.S. Army Pacific & Hawaiian Air Materiel Area – Would assist in the placement of seismic monitoring stations.
* Pacific Fleet – would provide naval security and operational support.
* Army Security Agency – Would establish security and communication protocols.
* 308th Reconnaissance Group (Weather) – Would aid in meteorological tracking and balloon-based nuclear debris detection.

### Secure Coded Communication

On March 9, 1948, Lieutenant General John E. Hull, Commander of JTF-7, and Major General William E. Kepner, Deputy Commander of JTF-7, held a high-priority meeting with Col. Nelson P. Jackson, assigning him the task of establishing a secure coded messaging system to transmit the nuclear detonation countdowns and the test results without exposing classified data. Col. Jackson devised a system of dummy-coded messages and time signals to ensure secure and covert communication of sensitive information.$^{:185,202,203,235}$

### Operations Plan Deployment and Development (March 13–March 21, 1948)

* March 13, 1948 – Col. Jackson and his team board the USS Mount McKinley, the flagship of JTF-7, departing for Eniwetok Atoll.
* March 16, 1948 – They arrive at Eniwetok and begin setting up Fitzwilliam Forward, the operational hub.
* March 17–18, 1948 – Col. Jackson conducts a command post exercise aboard the USS Mount McKinley, simulating real-world detection and response procedures.
* March 21, 1948 – Col. Jackson finalized and published Operations Plan Serial No. 1-48, the official document governing Fitzwilliam operations.$^{:185,202,203,235}$

## Scientific Involvement

With the decision in January 1948 to integrate long-range nuclear detection experiments into Operation Sandstone, Dr. Ellis Johnson, Technical Director of AFMSW-1, began assembling a team of top scientific experts. He coordinated with existing Air Force research units, university laboratories, and private research firms to leverage their expertise. All the science teams that made up Operation Fitzwilliam were members on contract from either Watson Laboratory, Tracer Labs Inc, Columbia University or New York University NYU.

### Chief Scientists

Dr. Ellis Johnson, a former professor at the Massachusetts Institute of Technology (MIT), was a leading authority in measuring and analyzing the Earth's magnetic vector. Since 1942, he had served as Associate Director of Research at the Naval Ordnance Laboratory (NOL), where he played a pivotal role in developing underwater mines, torpedoes, and countermeasures. In addition to overseeing the scientific team, Johnson was directly responsible for geophysical detection efforts.
Dr. Doyle L. Northrup, already involved in airborne radiological detection research, was tasked with developing the airborne fallout sampling network. Dr. Northrup was also a former MIT professor who had assisted Dr. Robert J. Van de Graaff on his giant electrostatic generator that was used in nuclear research. He had also been with the Naval Ordnance Laboratory (NOL) for many years collaborating with Dr. Ellis Johnson. Northrup would go on to be the Technical Director of the newly established AFOAT-1 (Air Force Office of Atomic Energy).
Dr. William D. Urry was another scientist from MIT that was tasked with overseeing radiochemical analysis of airborne nuclear debris.
Dr. J. Allen Crocker who had worked with J. Robert Oppenheimer and Enrico Fermi at the Los Alamos Scientific Laboratory and the University of California as part of the Manhattan Project, was assigned to seismic monitoring, working on the placement of detection equipment at various stations.
Dr. Donald H. Rock was included as an expert in airborne radiological detection instruments.

### Integration of Project Mogul Scientists

In March 1948, it was determined that high-altitude balloon-based sampling could complement airborne aircraft collection by detecting radioactive particles in the upper atmosphere. Since the Air Force already had a classified balloon surveillance program (Project Mogul), several scientists were transferred to Fitzwilliam. Project Mogul was a classified effort to develop high-altitude balloons for nuclear detection, which led to the 1947 Roswell UFO Incident. They were renamed as “Project Blackheart” for Operation Fitzwilliam. These scientists included:
Dr. James A. Peoples – The team leader and a specialist in high-altitude nuclear debris collection, Peoples was placed in charge of the balloon sampling network.
Dr. Charles B. Moore – A meteorological engineer, Moore worked on upper-atmospheric nuclear debris tracking and high-altitude wind pattern modeling.
Dr. Albert P. Crary – A geophysicist and polar research expert, Crary was brought in to refine acoustic and seismic monitoring systems. Crary later became a key figure in polar exploration, conducting research in both the Arctic and Antarctic.
Dr. Charles S. Schneider – An expert in atmospheric physics, Schneider adapted Project Mogul’s tracking systems for Fitzwilliams’ purposes.

## Nuclear Detection Methods

Operation Fitzwilliam deployed a comprehensive network of aircraft, balloons, ground stations, and ships to track nuclear debris and collect radiological data. A total of twelve B-29 Superfortress aircraft were utilized for airborne sampling, tracking, and reconnaissance missions. These aircraft were assigned to various units, including the 308th Reconnaissance Group (Weather) based at Fairfield-Suisun AFB in California, and the 373rd, 374th, and 375th Reconnaissance Squadrons, which conducted cloud sampling. The aircraft were launched from key locations such as Kwajalein, Barber’s Point in Hawaii, Guam, and Hickam Field.

### Drone Aircraft

In addition to crewed aircraft, drone aircraft were also employed to collect radiological samples from within the radioactive clouds produced by the nuclear detonations. These drones were remotely piloted from mother planes, ensuring they could safely navigate through highly radioactive areas too dangerous for human crews. Specially trained "beeper pilots" aboard the mother planes controlled the drones, guiding them through the nuclear cloud and back for sample retrieval. Pre-test training operations refined these control techniques, with practice flights and landings conducted at Eniwetok.

### The Bug Catcher

The “bug-catcher” system was a component of Operation Fitzwilliam. This system consisted of two separate devices mounted on B-29 aircraft, each holding a slab of activated charcoal measuring 9 x 22 inches, sandwiched between two layers of open-mesh wire screen. These filters were used to trap radioactive particles present in the upper atmosphere following a nuclear detonation. It functioned on the principle that nuclear explosions lift radioactive debris into the atmosphere, where it condenses around dust particles and is carried by prevailing winds. If these particles traveled far enough and remained in high enough concentrations, the filters could collect them for chemical analysis upon return.

### High Altitude Balloons

Fitzwilliam relied on an extensive balloon deployment strategy. Each monitoring station was instructed to release eight balloons per atomic explosion, resulting in a total of at least twenty-four launches per station across the three nuclear tests. The balloon stations were positioned at Majuro Atoll, Rongerik Atoll, and aboard the USS Quick and USS Davison, which served as mobile monitoring platforms. Each station maintained a supply of twenty-seven balloons, with three reserved for practice launches to ensure proper deployment. These balloons were equipped with radiosonde transmitters capable of relaying data from distances up to 150 miles, providing crucial high-altitude radiological tracking.

### Ground-Based Monitoring

Ground-based monitoring stations were established at strategic locations, including Majuro Atoll, Rongerik Atoll, Wake Island, and Kwajalein Atoll. To enhance the mobility of the detection efforts, the USS Quick and USS Davison were positioned approximately 600 miles northeast of Eniwetok to track nuclear debris as it dispersed. The stations were equipped with advanced detection instruments, including Naval Research Laboratory (NRL) automatic radiological counters, ground-based air-filter units, tray-type counters, and Esterline-Angus traffic time recorders. Additionally, 500 sheets of U.S. Army Chemical Corps filter paper were used to collect radioactive particles from the atmosphere for further analysis.

### Acoustic Monitoring

The acoustic detection network consisted of multiple sensor arrays positioned across vast distances. One network included six stations distributed from Kyoto, Japan, to Frankfurt, Germany. A second system comprised three large sensor arrays positioned approximately 1,000, 2,000, and 4,000 miles from the detonation site. Additionally, a third network of sixteen to twenty acoustic arrays was placed at distances ranging from 50 to 2,000 miles, with a specialized station in Washington, D.C. To complement these ground-based systems, two airborne balloon stations located at 400 and 1,000 miles from the test site were equipped to measure air pressure fluctuations at altitudes of up to 50,000 feet.

### Seismic Monitoring

Seismic monitoring was another critical component of the detection efforts. Eight seismographs were positioned at distances ranging from 250 to 1,000 miles from the nuclear test site, with an additional four located on the atoll itself. These stations recorded seismic activity generated by the detonations, which was further supplemented by data from U.S. Coast and Geodetic Survey permanent seismograph stations equipped with suitable instrumentation.

### Unconventional Detection Methods

Scientists at Los Alamos, located 5,000 miles from the test site, attempted to detect subtle shifts in the sky’s brightness following the detonation. Meanwhile, at Kwajalein, researchers investigated a proposed “ionospheric dimple,” a disturbance in the upper atmosphere that could potentially be identified through radio-wave interference. Lastly, two Army Signal Corps teams, positioned telescopes with photoelectric sensors at Guam and Eniwetok, aiming to capture any reflected light from the blast bouncing off the moon’s surface.

## Detection Testing During Atomic Detonations
### X-RAY Detonation – April 15, 1948

At 18:17 GMT on April 15, 1948, the first test of Operation Sandstone, designated X-RAY, was detonated from a 200-foot steel tower on Eniwetok Atoll. The explosion produced an atomic cloud that ascended to approximately 36,000 feet. As the cloud expanded, reconnaissance aircraft were dispatched from Joint Task Force 7 (JTF-7) to track its movement and collect airborne samples.
The meteorological team, using isentropic surface models, traced the cloud trajectory across the Pacific. The radiological tracking was performed using high-altitude flights, with detection flights extending up to 30,000 feet. Initial sampling revealed positive radioactive detection in designated flight paths. The primary cloud exhibited significant lateral dispersion, and tracking efforts continued as the cloud migrated eastward.
By analyzing fallout patterns, backtracking studies were performed to simulate potential long-range detection applications. Aircraft assigned to the operation were instructed to monitor wind trajectories to estimate how nuclear debris would travel globally.

### YOKE Detonation – April 30, 1948

At 18:09 GMT on April 30, 1948, the second test, YOKE, was successfully detonated. The explosion generated a cloud that reached an altitude of approximately 55,000 feet, significantly higher than X-RAY. This altitude difference impacted the subsequent dispersal patterns and influenced detection strategies. The meteorological team noted that upper-level winds carried the radioactive material in an easterly direction.
Aircraft from the 308th Reconnaissance Group were deployed to track the dispersal, with support from ground-based stations in Hawaii, Guam, and the U.S. West Coast. The radiological detection teams reported continuous tracking of the primary cloud mass, identifying its leading and trailing edges.
Unlike X-RAY, remnants of the YOKE cloud persisted in the region longer, influencing subsequent sampling missions. Long-range detection aircraft stationed at Midway, Bermuda, and as far as the Azores were activated to monitor potential residual traces as the cloud migrated across the globe.

### ZEBRA Detonation – May 15, 1948

At 18:04 GMT on May 15, 1948, the third and final test, ZEBRA, was detonated. The resulting cloud reached only 33,000 feet, making it the lowest-altitude detonation of the series. This unexpected altitude presented complications for planned detection efforts, particularly for balloon-borne sampling programs designed to operate at 50,000 feet.
Meteorological forecasts had predicted that the ZEBRA cloud would move toward California, prompting modifications to reconnaissance tracks originating from Fairfield-Suisun Air Force Base. Ground-based detectors were also repositioned, with a sensor array relocated to Sonora Pass, California, to attempt detection at higher elevations. However, these adjustments yielded no significant data.
Aerial reconnaissance flights attempted to track the ZEBRA cloud from Bermuda and the Azores, but no definitive readings were obtained. The lack of detectable signatures led to uncertainty regarding whether the cloud had reached the U.S. West Coast at all.

## Results of Operation

On May 13, 1948 Major General Kepner returned to Washington, D.C. and assigned Col. Nelson P. Jackson as Commander of Operation Fitzwilliam. Jackson would oversee the Zebra detonation test and would conduct all the post-test briefings to senior military and government officials.$^{:306}$
The briefings included detailed reports on the successes, challenges, and technical outcomes of the operation. The primary findings presented highlighted that through a combination of airborne particulate sampling, radiochemical analysis, and meteorological tracking, it was confirmed that radioactive particles could be detected thousands of miles from the detonation site.
The airborne detection techniques from specially modified B-29 aircraft had worked effectively. The aircraft, equipped with filter paper devices, had captured fission particles at various altitudes and locations and the filters successfully retained radioactive material, which was then analyzed at field stations for isotopic identification.
Ground-based monitoring stations had also been successful in detected nuclear debris, confirming that fallout could be tracked over extended periods.
The radiochemical analysis of the collected samples had proved conclusive in identifying fission products, including Cesium-137, Strontium-90, and Xenon-133, all of which are direct indicators of a nuclear detonation. The gross decay rates of these isotopes were able to be measured to verify their origins. The operation also validated meteorological models, demonstrating that the movement of radioactive clouds could be predicted based on wind patterns and atmospheric conditions. This confirmed that nuclear debris could travel thousands of miles, a fact later used to detect Soviet atomic tests.
The analysis of seismic waves indicated that existing seismographs were incapable of detecting an airburst explosion at long range, as signals were only observed within 500 miles of the test site. These signals had a velocity consistent with transmission through water, suggesting that seismic data could be highly effective for detecting underwater and underground nuclear detonations.
Despite Operation Fitzwilliam's successes, it faced technical challenges. Aircraft contamination was a persistent issue, with some planes remaining radioactive for weeks after exposure to nuclear debris. The filter systems were effective but required improvements, as some tests showed incomplete collection or inconsistent data due to variable atmospheric conditions. Seismic and acoustic detection methods, tested alongside airborne sampling, proved ineffective for high-altitude nuclear detonations. Additionally, data gaps emerged due to limitations in flight scheduling and coverage, making some cloud reconstructions incomplete.

## Outcome and Legacy

The intelligence obtained from Operation Fitzwilliam led to the creation of the Atomic Energy Detection System (AEDS). Less than a year later, Doyle L. Northrup the Technical Director of the newly established AFOAT-1 (Air Force Office of Atomic Energy) successfully detected the Soviet Union’s first nuclear test using these methods. Many of the techniques developed in Operation Fitzwilliams were later used in the Partial Test Ban Treaty monitoring system.