The result of his new efforts was the Lambertsen Amphibious Respiratory Unit II (LARU II). It featured a more robust design, and a new air recirculating arrangement that made carbon dioxide removal more efficient.

A second NEDU demonstration was scheduled for April 1942, and this time, in addition to Navy personnel, representatives from the British Special Operations Executive (SOE) and U.S. Office of Strategic Services (OSS) were on hand. Both agencies had been looking for an underwater breathing apparatus that would enable frogmen to conduct long-term, covert underwater missions in littoral waters, and the men saw in Lambertsen’s unit the answer to their needs. Encouraged by what they saw, the OSS arranged to have Lambertsen work for them during his senior year. Upon his graduation from medical school in June 1943, Lambertsen tried to enlist in the Navy but was rejected because he suffered from hay fever. The OSS, however, was willing to look past his allergy affliction. Lambertsen was recruited by the OSS, commissioned a first lieutenant in the Army Medical Corps, and assigned to its new OSS Maritime Unit (OSSMU), where he would both continue work on his underwater breathing apparatus and train swimmers in its use.

The aspect that made the Lambertsen Unit particularly attractive to the OSS and SOE was its rebreather capability. The carbon dioxide scrubber, consisting of soda lime, not only allowed the frogman to reuse the oxygen in the self-contained system, but did not leave any tell-tale exhaust air bubbles like conventional scuba equipment.

One member of the OSSMU was the legendary Jack Taylor. A naval reservist, then-Lt. Taylor was one of the first three officers posted to the OSSMU when it was formed in early 1942. He began training in “Area D,” an OSS training facility on the shore of the Potomac River directly across the river from the Marine Corps base at Quantico, Va. In addition to training, the men tested a variety of equipment, including the new Lambertsen Amphibious Respiratory Unit III (LARU III). Two underwater swimming groups, called “L-Units,” were subsequently formed. During one test of the LARU III during this period, Taylor remained underwater for more than 48 minutes and swam more than one mile, at the time an extraordinary achievement. Taylor would subsequently go on to conduct missions in the Mediterranean and Middle Eastern theater of operations. Captured while conducting Operation Dupont – a mission in Austria to try and establish resistance cells – at the end of November 1944, he was taken to the Mauthausen concentration camp. He was liberated by Soviet troops on May 5, 1945. Taylor would receive the Navy Cross for his participation in Operation Dupont. He was promoted to the rank of lieutenant commander and was a witness at the Nuremburg war crimes trials before being discharged.

By May 1944, the OSSMU had organized three Operational Swimmer Groups (OSG), totaling 226 personnel. Declassified records revealed that it was a joint service effort, with men from the Army, Navy, Marine Corps, and Coast Guard. It even included four civilians in its ranks. It was now time for a full-scale, dress-rehearsal exercise to see whether or not all the planning and training really worked.

Code-named Operation Cincinnati, it was the first exercise of its kind designed to test shore defenses protecting military facilities – in this case the U.S. Navy’s harbor defenses in Guantanamo Bay, Cuba. As such, it pre-dated by almost 40 years the Red Cell teams of SEAL Team Six formed in 1984 for the same purpose.

As detailed in Operational Order #5, the mission of Operation Cincinnati was for four teams of nine men each (designated Red Group, Blue Group, Black Group, and Orange Group) to enter the harbor and “destroy 4 enemy ships between the hours of 2000 and 2400 on 21 July 1944.” In addition, the groups were ordered to “preserve the highest degree of secrecy and security in connection with all phases of this attack and in particular concerning the method of attack.”

The exercise commenced at 2015 (8:15 p.m.) when the four groups boarded their 50-foot mother ship laden with their equipment, which included Lambertsen Units for each man. The Lambetsen Unit was not the only piece of equipment being tested in the exercise. Each group was assigned different transportation equipment and vessels, the goal being to determine the suitability of each. Group Red had rubber paddleboards, Group Blue two-man kayaks, Group Black a seven-man rubber boat, and Group Orange a “flying mattress.”

Operation Cincinnati was a success. All the teams performed their assigned tasks without detection. In his evaluation, OSS operative Kermit Roosevelt wrote, “In these tests, the lengthy training showed commendable results, because the swimmers were able to circumvent the net defenses in each instance. An additional point of value was proof that the Navy sound detection gear did not reveal the presence of underwater swimmers.”

Field deployment began in January 1944, with units sent to Europe and the China, Burma, India (CBI) theater. From bases in Italy, operations in the Mediterranean were conducted in the Adriatic and Aegean seas and ran the gamut. They included maritime sabotage, sneak attacks, ferrying weapons, agents, and supplies to resistance units and evacuating downed fliers and refugees from occupied territories. Teams based in England conducted similar operations in Scandinavia.

In the CBI, teams were stationed in Ceylon (present-day Sri Lanka), Burma, and India. Most of the operations involved intelligence gathering. One particularly harrowing mission in the CBI was Operation Cleveland, conducted on Jan. 25, 1945. In addition to obtaining intelligence of the target area, including a survey of the coastline, terrain, and strength and status of enemy forces in the area, it also included the capture of a native, or an enemy soldier, for purposes of interrogation. Needless to say, the most difficult aspect of the operation was the live capture and exfiltration of an enemy soldier. The team accomplished every aspect of the difficult mission, including the capture of an enemy soldier.

Meanwhile, the SOE had developed the Sleeping Beauty, an underwater one-man craft similar to the one-man submarines used by Italy’s 10th Light Flotilla. Lambertsen’s involvement with the Sleeping Beauty started in January 1944, when an L-Unit returned from England after having trained with SOE teams for missions in support of D-Day, which were canceled because mission requirements proved to be beyond the teams’ capabilities. The teams brought with them a Sleeping Beauty and Lambertsen, by now a captain, immediately developed doctrine and procedures for its use. His work in this area continued after he was stationed in Ceylon and given two Sleeping Beauties to work with. His work with the Sleeping Beauty, eventually became the foundation for the swimmer delivery vehicle concept.

Lambertsen was discharged from the Army in 1946 with the rank of major. Though a civilian and working at the University of Pennsylvania Medical School, Lambertsen’s role with special operations was not over. By now, the OSS had been disbanded and it looked like the Navy’s special operations Underwater Demolition Team (UDT) program would soon follow. Lt. Cmdr. Francis Douglas “Red” Fane was in charge of two reduced-strength UDT teams stationed in Little Creek, Va. Wanting to save the force from demobilization, he contacted a number of scientists and experts in the field. A key member of this group was Lambertsen. Lambertsen was instrumental in developing new and innovative doctrine and training for UDT swimmers that increased their mission capabilities and helped save the unit from administrative extinction.

Lambertsen would go on to have a distinguished career in medicine. In 1968, he founded the Institute for Environmental Medicine at the University of Pennsylvania. He also received numerous military and civilian decorations and honors, among them the Presidential Unit Citation for service in Burma with OSS Unit 101, the Legion of Merit, and Honorary Lifetime Membership in the UDT-SEAL Association and the OSS Society’s Distinguished Service Award.