Guides: W. Bruce Fye Center For the History of Medicine: Top Secret: Mayo Aeromedicine and Operation Paperclip

Mayo Clinic's Aero Medical Unit [left column]

In the 1930s, newly designed aircraft were able to fly higher than 10,000 feet. Pilots at this altitude were at increased risk of hypoxia, a condition in which the body’s tissues are starved of oxygen leading to fatigue and blackout. This was an increasingly significant factor in pilot error and plane crashes worldwide. Mayo Clinic and commercial airlines began researching solutions to this problem.

During World War II, Mayo Clinic created the Aero Medical Unit. They built pressure chambers, a centrifuge, and a cold chamber to study the effects of altitude and G-force on the human body. The Unit conducted research with Army and Navy pilots to develop the BLB oxygen mask, G-suit, and bail-out bottle that allowed pilots to fly faster, higher, and make more maneuvers in the air. These developments proved instrumental in the war effort.

Key personnel

Walter M. Boothby, M.D.

Dr. Boothby was born in 1880 and joined Mayo Clinic in 1916 as head of the Section of Metabolism. He became chair of the Mayo Clinic Aeromedical Unit in 1942 and was involved in the construction of oxygen chambers used to simulate high elevation respiration, hosted pilots as part of a high-altitude indoctrination program, and helped develop both the G-suit and BLB mask used in WWII. Dr. Boothby retired from Mayo Clinic in 1948 and died in 1953.

E. J. Baldes, Ph.D.

Dr. Baldes was born in 1898 and joined Mayo Clinic in 1924 as first assistant in the Section of Biophysics and Biophysical Research, becoming head of the section in 1948. He became widely known for his studies of the physiologic effects of acceleration in aviation. During WWII, he planned and supervised construction of Mayo Clinic's human centrifuge for acceleration studies. He was a special consultant to the U.S. Air Force Aeromedical Laboratory at Wright-Patterson Air Force Base in Dayton, Ohio, from 1942 to 1954. Dr. Baldes retired from Mayo Clinic in 1963 and died in 1975.

W. Randolph Lovelace, II, M.D.

Dr. Lovelace was born in 1907 and joined Mayo Clinic in 1936. He became a flight surgeon in 1937 and became Dr. Charles W. “Chuck” Mayo’s first assistant in surgery in 1939. Dr. Lovelace then transferred to oxygen research at Mayo where he developed the BLB mask alongside Drs. Boothby and Bulbulian. He was active duty in the U.S. Army Air Force from 1942-1945 during which time he became chief of the Army Aeromedical Research Laboratory at Wright Field, Ohio. He left Mayo Clinic in 1946 to join the Lovelace Clinic in Albuquerque, New Mexico and died in 1965.

Charles F. Code, M.D., Ph.D.

Dr. Code was born in 1910 and joined Mayo Clinic in 1934. He became a consultant in the Department of Physiology in 1940. His special interests included histamine, aviation medicine, and cardiovascular and gastrointestinal physiology. He worked to establish a closer relationship between science research and clinical medicine as practiced at Mayo and directed the physiological experiments on the centrifuge that resulted in the creation of the G-suit. Dr. Code retired from Mayo in 1975 and died in 1997.

Earl H. Wood, M.D., Ph.D.

Dr. Wood was born in 1912 and joined Mayo Clinic in 1942 as a research assistant. Working with colleagues in Mayo Clinic’s Aero Medical Unit, Dr. Wood studied the methods for prevention of pathophysiologic effects of positive acceleration experienced by fighter and dive bomber pilots during WWII. Using the Mayo human centrifuge, he and his colleagues developed the G-suit for the prevention of blackout in pilots. He also developed the M-1 maneuver, an exhaling technique for pilots to prevent blackouts. He retired from Mayo Clinic in 1982 and died in 2009.

Arthur H. Bulbulian, D.D.S.

Dr. Bulbulian was born in 1900 and came to Mayo Clinic in 1933. He was appointed director of the Mayo Medical Museum in 1935. As head of maxillofacial prosthetics, Dr. Bulbulian carried out extensive studies on the restoration of missing parts of the face and head. These skills were invaluable in helping to design the BLB oxygen masks. Dr. Bulbulian retired from Mayo Clinic in 1965 and died in 1996.

Edward H. Lambert, M.D., Ph.D.

Dr. Lambert was born in 1915 and joined Mayo Clinic in 1943 in the Department of Physiology. He was an investigator in Mayo Clinic’s aerospace research program. In 1947, he received the U.S. President’s Certificate of Merit for work on the effects of acceleration in humans which led to the development of the G-suit used by allied air forces in WWII and space suits used by NASA astronauts. Dr. Lambert retired from Mayo Clinic in 1985 and died in 2003.

High altitude pressure chamber

One of Mayo Clinic’s high altitude pressure chambers, circa 1942.

Mayo Clinic researchers built a pressure chamber to simulate the high altitudes pilots endured. On March 26, 1939, Mayo Clinic’s pressure chamber, the first civilian high altitude chamber in North America, made its first “flight” to 15,500 feet. This gave Mayo Clinic researchers new understanding of the pathophysiology of hypoxia and decompression sickness at high altitude. The work produced a series of high-altitude oxygen masks (BLB masks) which were used during and after the war to protect pilots from oxygen deficiencies.

Aero Medical Unit technician Lucille Cronin sitting at the door of a high altitude pressure chamber, 1941.

Centrifuge

Dr. Earl H. Wood (right) and unidentified man in the centrifuge, 1946.

In 1942, Mayo Clinic built a human centrifuge in the basement of the Medical Sciences Building. The centrifuge was capable of simulating the high G-forces encountered in flight which led to pilot blackout and unconsciousness. The classified studies produced fundamental knowledge that led to the production of anti-gravity or “G”-suits for WWII fighter pilots. Drs. Charles F. Code, Edward H. Lambert, and Earl H. Wood repeatedly served as experimental subjects on the centrifuge.

Diagrammatic section drawing of Mayo Clinic’s centrifuge, 1943.

Comic that appeared in the September 5, 1959 issue of Mayovox.

G-suit

Early prototype of the G-suit, 1941 (left) and improved design, 1945 (right).

With the help of David Clark of the David Clark Company, Mayo Clinic created the G-suit, a garment designed to combat the forces that kept blood from being pumped to the brain during high-speed maneuvers. As centrifugal forces on the pilot climbed above 1.5 G, bladders on the suit were automatically pumped full of air, restricting the flow of blood from the abdomen to the lower extremities thereby maintaining arterial pressure to the head. Its basic design is still in use today in modern fighter aircraft.

BLB Mask

Patent drawing of an oxygen mask invented by J. D. Akerman, Dr. Boothby, and Dr. Bulbulian, circa 1940.

The BLB mask, named after its designers, Dr. Walter M. Boothby, Dr. W. Randolph Lovelace, and Dr. Arthur H. Bulbulian, was initially developed as part of Mayo Clinic’s response to an inquiry from Northwest Airlines regarding the efficacy of providing oxygen during regular passenger service at high altitudes. An increase in commercial airline crashes was attributed to “pilot error” due to newer airplanes flying above 10,000 feet. This altitude led to hypoxia, causing pilot fatigue. The first BLB mask was created at Mayo Clinic in February 1938.

At the solicitation of the U.S. Air Force in the early 1940s, the Mayo team modified the BLB mask and its oxygen equipment many times to meet the special needs of the military, resulting in the A-14 mask. This included making it frost-proof and equipped with a microphone for radio intercommunication. In the decades following WWII, the A-14 mask was a prototype for all subsequently developed military and medical oxygen masks.

A-14 mask mold, circa 1940s

This mold (left) for the A-14 came from Dr. Bulbulian’s personal collection of oxygen mask-related items. The mask displayed with it is a military surplus example.

Called a “benchmark” in oxygen mask development, the A-14 mask was modified by Dr. Arthur Bulbulian from earlier versions of the BLB mask. It made its combat debut in 1943 and was so well-designed that improved models remained in regular use well into the 1980s.

Bailout bottle, circa 1940s

To stay conscious at high altitudes, aviators abandoning an aircraft needed an emergency supply of oxygen. Mayo Clinic designed a bailout bottle that could easily be attached to the pilot and activated upon leaving the plane. The end of the tube not connected to the bottle could be attached to the face mask. The bailout bottle was tested in numerous simulated parachute jumps in the altitude chambers in Rochester.

Aero Medical Unit personnel wearing the BLB mask and bail-out bottle, 1942.

Women in the Aero Medical Unit

The studies conducted in Mayo Clinic’s Aero Medical Unit were considered top secret and only individuals vetted by Mayo Clinic’s newly created Security Section were allowed access to the Unit. Specific Mayo staff members were issued photo identification cards that were required for admission. A number of women worked in the Unit, many of whom trained in Dr. Boothby’s Metabolic Lab, worked through the war, and continued to have long careers at Mayo Clinic.

Rising to the Challenge: The Mayo Aero Medical Unit in World War II

The 2023 Heritage Days movie highlights the multi-faceted research done in Mayo Clinic’s Aero Medical Unit. It contains footage from newly transferred film reels held in the Mayo archives. The movie can be viewed on the Video Exchange and on Mayo Clinic’s History & Heritage external facing site.

Aeromedicine films

The W. Bruce Fye Center for the History of Medicine has over 1,500 reel-to-reel films in its collections. Over the years, many have been transferred to digital format. The Center identified numerous films related to aeromedicine. With the help of Heritage Days, these films were then digitized at high resolution. Clips from many of these films can be seen in the new Heritage Days film described above.

Life at High G-Force

Life at High G-Force: The Quest of Mayo Clinic Researcher Dr. Earl H. Wood by E. Andrew Wood, 2023

Dr. Earl Wood’s son, E. Andrew Wood, recently published a biography about his father that includes his experience in Mayo Clinic’s Aero Medical Unit. Published by Mayo Clinic Press, it can be purchased online at https://mcpress.mayoclinic.org.

Operation Paperclip [right column]

At the end of 1945, Drs. Edward J. Baldes and Earl H. Wood joined Operation Paperclip, a secret U.S. government program aiming to salvage German scientific research. American advisors like Dr. Baldes traveled to Germany and met with scientists, examined facilities, and purchased necessary equipment and supplies for the continuation of vital projects. As part of the mission, thousands of German scientists and engineers—such as Wernher von Braun—were brought to the United States.

Born in 1898 to a German American family in Nebraska, Dr. Baldes joined Mayo Clinic’s Section of Biophysics and Biophysical Research in 1924. During World War II, Dr. Baldes’ work focused on the effects of acceleration, and he designed a human centrifuge to aid Mayo Clinic’s aeromedical research.

In September 1945, Dr. Baldes received orders to go to Germany, which he visited between October 1945 and May 1946. Based at the Army Air Forces (AAF) Aero Medical Center in Heidelberg, he met several German aeromedical experts and purchased scientific equipment for the continuation of their research. Dr. Baldes was struck by the state of postwar Europe, often noting the hardships the civilian population faced.

Operation Paperclip ran through the 1950s, but it is not clear whether Dr. Baldes participated beyond his 1945-46 visits to Germany. He served as special consultant to the USAF Aeromedical Laboratory at Wright-Patterson Air Force Base in Dayton, Ohio until 1954.

Back in Rochester, Dr. Baldes served as head of the Section of Biophysics and Biophysical Research from 1948 to 1958. During the 1955-56 school year, Dr. Baldes and his wife opened their home to Christa Bungener, a Lourdes High School exchange student from Olpe, Germany.

Dr. Edward J. Baldes, 1946

This photograph shows Dr. Baldes on the grounds of the AAF Aero Medical Center in Heidelberg.

Flight Surgeon’s German-English Glossary, undated

Cover of Flight Surgeon's German-English Glossary

This aviation glossary belonged to Dr. Baldes (note “EJB” penciled on the cover).

Introduction of Flight Surgeon's German-English Glossary

Page from Flight Surgeon's German-English Glossary

List of former fellows and students, 1946

This list of former Mayo Clinic fellows and students was compiled for Dr. Baldes in March 1946. The information was out of date: Dr. Precht had died in Hamburg in 1938, and the expulsion of ethnic Germans from the Prussian and Silesian provinces in 1945 affected the residences of Dr. Dorffel (Königsberg/Kaliningrad, Russia) and Dr. Bernhardt (Ratibor/Raciborz, Poland). However, Dr. Baldes was able to track down Dr. Formijne during a trip to the Netherlands in May 1946:

We were able to get the wife of Doctor Formijne on the phone, and we made arrangements to go on to Amsterdam to visit them that evening…. They displayed the little stove on which they cooked…during the starvation period which lasted about three months. First they lived in a single room and then moved into another room, much smaller, in order that they might keep warm…. The caloric intake was 300 calories a day…. Doctor and Mrs. Formijne very kindly put us up at night and served breakfast to us the following morning. Although conditions are much better in Holland, it is obvious that it is very difficult to purchase food. -- Edward J. Baldes

Amsterdam, June 1946.
Courtesy of Nationaal Archief.

Meeting notes, December 1945

This report summarizes a meeting between Dr. Baldes and German engineers at the Städtisches Werk Tegel (formerly Borsig), Berlin, to discuss the construction of a cooling system. The notes underscore the instability of industry immediately after the war, from lost designs to unavailable materials, while the mention of the American sector (one of the four postwar occupied zones) foreshadows the impending political and physical division of West and East Germany.

[See translation on next 2 slides]

On Sunday 12/1 and on Wednesday 12/5/45, we were visited by Dr. Baldes of American aviation, Heidelberg, and Dr. Luft from the university, Berlin.

In Heidelberg, Dr. B. had a conversation with Dr. Ruff, who for the time being is working there with the Americans. Because of this, Dr. B. approached us to ask whether we are currently in a position to supply a cooling system exactly like the system ordered by the German Research Institute for Aviation, Adlershof, for a total output of 18000 cal/h at an average temperature of -124 Celsius.

We explained to Mr. B. that we are, with certain limitations, in a position to design such a system. However, the project planning has to be done from scratch, since all the documents were lost. Therefore, a general meeting in Heidelberg between Dr. Baldes, Dr. Ruff, Dr. Linge and us would be recommended.

The cooling system for -80 Celsius was discussed with Dr. B. on the basis of an existing drawing, B 801-5818. The project planning of this cooling system would take about 1/2 year with 5 designers. The costs for this are approximately RM 100000, up to RM 150000. The costs are of course for the delivery of all design documents and piping diagrams, including operating instructions in triplicate for the above-mentioned plant. However, we propose to charge the construction hours at the following rates:
RM 12.50/hour for the designers and engineers
RM 25/hour for the chief engineer

We could currently produce the following machines and apparatus in our factory ourselves:
both air compressors type SKLZV 225,
1 filling compressor for 120 cbm/h,
2 air coolers for 100 and 200 ata and all oil separators.

On the other hand, the following would have to be made in America according to our construction plans:
the heat exchanger 40 cm, which must be made entirely of copper and bronze,
the second heat exchanger for the vacuum pump unit, which is made of aluminum,
the cooling systems,
the pressure chamber,
the air lock,
the vacuum chamber,
the Silica gel dryer and all the fittings.

The two vacuum pumps, each with a capacity of 800 cbm/h for a suction pressure of 0.1 ata and a back pressure of 1 ata, would be ordered from Siemens. We first have to find out whether Siemens is now in a position to supply them. Otherwise, the pumps have to be procured in America as well.

Should it be necessary to open an engineering office in the American sector for the smooth execution of the design plans, space would have to be made available there. Dr. B. would also have to set up a liaison office so that mail could be sent by air as quickly as possible between Berlin and the headquarters in Heidelberg.

If the system has to be exported, we would still have to prepare a binding offer with precise delivery time specifications.

Dr. Siegfried Ruff

Dr. Siegfried Ruff on trial, November 21, 1946 (Courtesy of NARA)

Siegfried Ruff (1907-1989) was director of the Aviation Medicine Department at the German Experimental Institute for Aviation. He worked closely with Dr. Baldes to procure research equipment for aeromedical projects in postwar Germany. Dr. Ruff was indicted at the 1946-47 Nuremberg “Doctors’ Trial” for overseeing human aeromedical experiments at Dachau concentration camp; he was acquitted after arguing that the experiments took place in accordance with the law, adding in his affidavit, “I would not consider these experiments as immoral especially in war time.” He remained in West Germany and continued his career as head of the new Institute of Aviation Medicine and as professor at the University of Bonn.

In the second row to the far right is Dr. Hermann Becker-Freyseng (1910-1961), a member of Dr. Ruff’s staff who also worked at the AAF Aero Medical Center after the war. He was sentenced to 20 years imprisonment for war crimes and crimes against humanity.

Dr. Siegfried Ruff during the Nuremberg Trials, 1946-1947. (Courtesy of NARA)

Dr. Ruff and his staff. Report from Heidelberg.

L-R: Dr. Hermann Becker-Freyseng, Karl Hausser, Dr. Siegfried Ruff, Dr. Konrad Schaefer, and Dr. Otto Gauer.

Dr. Hubertus Strughold

Dr. Hubertus Strughold, 1946

Hubertus Strughold (1898-1986) was head of aeromedical research in the Nazi Ministry of Aviation, led by Hermann Göring. He faced multiple allegations of war crimes relating to human experimentation at Dachau concentration camp but was never charged due to a lack of evidence. Dr. Strughold often acted as a liaison for Dr. Baldes, and Dr. Baldes reported lodging with various relatives of Dr. Strughold as they traveled together around Germany in May 1946. In 1947, Dr. Strughold moved to the United States under Operation Paperclip, becoming known as the “Father of Space Medicine”. This portrait from Dr. Baldes’ papers is simply captioned “Strugie”.

Dr. Strughold at work. Report from Heidelberg.

Dr. Strughold and his staff. Report from Heidelberg.

L-R: Mr. Johannes Prast, Dr. Ingeborg Schmidt, Dr. Heinz Haber, Dr. Strughold, Dr. Siegfried Gerathewohl, and Dr. Heinrich Rose.

Fundamentals of Aviation Medicine

Siegfried Ruff and Hubertus Strughold. Fundamentals of Aviation Medicine (second edition). Leipzig: J. A. Barth, 1944.

This book by Drs. Ruff and Strughold is from the W. Bruce Fye History of Medicine Library. Part of Mayo Clinic Libraries, the History of Medicine Library is a special collection holding several thousand medical and scientific publications dating back to 1479.

Inscription reads, "To Dr. H. Burchell with the best regards in Memory to Heidelberg. - H. Strughold, 3.9.48"

Howard B. Burchell (1907-2009) entered the Mayo Graduate School of Medicine in 1936 as a fellow in medicine and received a Ph.D. from the University of Minnesota in 1940; that same year, he was appointed a Mayo Clinic consultant in medicine. Dr. Burchell left Mayo in 1942 to serve in the U.S. Army Medical Corps (1942-1946) during World War II. Returning to Mayo in 1946, he was appointed a consultant in medicine and cardiology.

[See translation on next slide]

Contents
Forward to the first and second editions

Chapter I. The problems of aviation medicine in light of the historical development of aviation

Chapter II. Altitude
1.   Physics and chemistry of the atmosphere
2.   Extent and components of altitude
3.   Methods, systems and nomenclature
4.   Hypoxia
5.   Effects of total air pressure
6.   The flight with excess pressure
7.   The descent – parachute descent
8.   The altitude adjustment
9.   Radiation effect as an altitude factor

Chapter III. Acceleration
1.   Physical basics
2.   Velocity effect
3.   Straight line accelerations
4.   Radial accelerations
5.   Angular accelerations
6.   Airsickness

Chapter IV. Psychophysiology of flight

Chapter V. Flight hygiene and accidents
1.   Harmful liquids and gases
2.   Noise
3.   Vibrations
4.   Nutrition
5.   Cold protection
6.   Accidents

Chapter VI. Comparative flight physiology
1.   Physiology of bird flight
2.   Human-powered aircraft

Subject index

[illustration 12, p. 28]
Pressure chamber of the Aeromedical Research Institute of the Ministry of Aviation

[illustration 80, p. 163]
Centrifugal force in the vertical axis during a “roll”

[illustration 81, p. 163]
Centrifugal force in the vertical axis during a “forward loop”

[illustration 82, p. 163]
Trajectory of a spinning airplane

[illustration 85, p. 165]
Centrifuge of the Aeromedical Research Institute of the Ministry of Aviation

AAF Aero Medical Center, Heidelberg, 1946

American personnel and German scientists pose for a group photograph in the spring of 1946. Dr. Baldes is second from the left and Dr. Strughold is third from the right. The Americans next to Dr. Strughold are (right to left) Capt. Sydney Titelbaum, Col. Robert J. Benford, and Dr. Earl H. Wood.

Sourcing Equipment

List of scientific equipment needed, undated
As part of his survey of research facilities and projects, Dr. Baldes often needed to source necessary equipment and materials to enable the continuation of aeromedical research.

Receipt from Steeg and Reuter, May 1946
This receipt from Steeg and Reuter is for two heart sound microphones.

Cost estimate from Leitz Optical Works, June 1946
This Leitz document provides a price list for lighting, observing, and recording equipment.

Letter from Dr. Baldes, 1946
In the following letters by Dr. Baldes and Dr. Strughold, they inquire about the availability and cost of recording equipment such as kymographs and electrocardiographs.

[See translation of this letter on next slide]

Baldes Letter
17 May 1946
To
Zeiss-Ikon A.-G.
Schandauerstrasse 76
Dresden A 21

Re: Ikon-Kymograph-Camera

I received your address from the Carl Zeiss Company, Gaussstrasse 38, Stuttgart (Dr. Doerffler) with the recommendation to contact you directly.

Would you please let me know if, in the foreseeable future, you can deliver a complete Ikon-Kymograph-Camera. I am also very interested in individual parts of such a camera.

I would be grateful for a prompt reply to my inquiry.

Sincerely,

Letter from Dr. Strughold, 1946

[See translation on next slide]

Strughold Letter
Attn: Prof. Strughold, Heidelberg, Jahnstr. 1
Heidelberg, June 6, 1946

F. Hellige & Co.
Fabrik wissenschaftlicher Apparate
Freiburg im Breisgau

Thank you for your letter of May 15, 1946 – your reference Fri/Frs. –
At the same time, I would like to thank you on behalf of Prof. Dr. Baldes and Dr. Wood for the information we received during our visit 14 days ago.

I would now like to ask you to make us an offer with delivery time and price for the following devices:
1.   Kymograph
2.   Electrocardiograph
3.   Electrophoresis apparatus
4.   Gas exchange recorder and similar apparatus

I ask you to please send these offers, each on a separate sheet, to the address:
Aero Medical Center, Heidelberg, Jahnstr. 1.

I would be grateful if these offers could be in our hands soon, as the order should go out as soon as possible.

Best regards,

Meeting in Heidelberg, 1946

L-R: Drs. Hubertus Strughold, Edward J. Baldes, Earl H. Wood, and Theodor Benzinger discuss aeromedical projects at the AAF Aero Medical Center. Report from Heidelberg.

Theodor Benzinger (1905-1999) was a German physician and pilot whose research focused on high altitude flight and rapid decompression. He was recruited by Operation Paperclip in 1947 and worked for the U.S. Naval Medical Research Institute. In 1964, Dr. Benzinger invented the ear thermometer.

Dr. Benzinger and his staff. Report from Heidelberg.

L-R: Dr. Heinz Maier-Leibnitz, Dr. Charlotte Kitzinger, Dr. Benzinger, Henry Seeler, and Dr. Helmuth Beinert.

Dr. Benzinger's staff developed new airplane oxygen equipment and special techniques for measuring respiratory gases.

Reports, 1945-1946

This small sampling of Dr. Baldes’ papers demonstrates the scope of his investigations, from logistics and project prioritization to technical sketches collected during discussions with German scientists.

German product booklets, mid-1940s

Dr. Baldes collected several booklets showcasing German companies’ medical, scientific, and technical products.

Siemens
Metal detector for foreign body localization in surgery
The novel electroacoustic apparatus for fast, reliable detection of metallic foreign bodies of any kind, especially light metal splinters

Steeg & Reuter
Heart sound microphone for interference-free listening and recording of cardiac activity

Celodal
The new plastic for the preservation of biological preparations
Anatomy, zoology, botany, museums, collectors

W. Bruce Fye Center For the History of Medicine: Top Secret: Mayo Aeromedicine and Operation Paperclip

Top Secret: Mayo Aeromedicine and Operation Paperclip