Combat Diving: Turning The Tide Of War From The Void
Combat Diving: Warfare's Favorite Water Sport
The military use of diving long predates the invention of scuba. For centuries, sailors and soldiers entered the water for reconnaissance, salvage, sabotage, and the destruction of underwater obstacles. What changed in the twentieth century was the ability to remain underwater independently of the surface, transforming diving from a specialized maritime skill into a method of covert warfare.
The history of military diving is therefore best understood as a gradual progression: breath-hold diving, surface-supplied diving, rebreathers, open-circuit scuba, and finally the integration of diving with modern special operations.
The Origins of Military Diving
The earliest military divers had only one piece of equipment that could not be improved upon: their own lungs.
Ancient Mediterranean societies used divers for naval reconnaissance, salvage, and sabotage. Historical accounts describe divers being employed during ancient sieges to interfere with underwater obstacles and the anchors of enemy vessels. The principle was simple. A ship could defend itself against an enemy approaching across the water, but an individual swimmer approaching beneath the surface presented a very different problem.
This made underwater movement particularly valuable in naval warfare. A diver could cut a mooring line, investigate a harbor, remove an obstacle, or approach a vessel without presenting the silhouette of a conventional attacking force.
The limitation was obvious. The diver's endurance was measured in minutes rather than hours, unless of course... you didn't come back up.
For much of antiquity and the medieval period, military diving therefore remained a specialized and relatively primitive art rather than an independent branch of warfare.
The Diving Bell and the Age of Surface-Supplied Diving
The development of the diving bell began to overcome the limitations of breath-hold diving.
A diving bell carried a supply of trapped air beneath the surface, allowing its occupants to remain underwater for considerably longer periods. Later developments in pumps, helmets, air hoses, and diving suits eventually produced the familiar surface-supplied diver.
By the nineteenth century, naval diving had become an established profession. The U.S. Navy employed divers for salvage, ship repair, construction, reconnaissance, and other underwater work. The same general development was occurring in European navies.
These divers could remain underwater far longer than a breath-hold swimmer, but they remained physically connected to a vessel or other source of air.
That distinction mattered enormously in warfare.
A diver attached to an air hose could repair a ship or recover a wreck. He was much less suited to quietly entering an enemy harbor.
The military problem was no longer simply how to breathe underwater. It was how to do so while remaining mobile and, ideally, undetected. An issue we still to this day strive to fully dominate.
The First Modern Combat Divers
The First World War brought renewed interest in underwater sabotage.
Naval mines, submarines, coastal defenses, and heavily protected anchorages created opportunities for small underwater teams to accomplish what conventional naval forces could not.
Italy became one of the principal pioneers of this approach.
During the interwar period, Italian naval officers experimented with specialized underwater assault equipment, including human torpedoes and closed-circuit breathing apparatus. By the late 1930s, Italy had developed the Decima Flottiglia MAS, which would become the most famous combat-diving organization of the Second World War.
The importance of the period lies less in any single piece of equipment than in the emergence of a new military concept:
A diver could be an offensive weapon rather than merely an underwater technician.
The Rebreather
The development of the closed-circuit rebreather was one of the most significant technological advances in military diving.
Ordinary open-circuit scuba releases exhaled gas into the water, producing the familiar stream of bubbles. A closed-circuit system instead recycles the diver's exhaled gas, removing carbon dioxide and replenishing oxygen as necessary.
The result was not simply greater endurance. It offered something considerably more valuable to a military diver:
concealment.
A diver operating beneath a harbor could potentially move without leaving a visible trail of bubbles on the surface.
This principle had been explored in various forms before the Second World War, but it was during that conflict that closed-circuit diving became a practical military technology.
World War II
The Second World War marked the decisive emergence of the modern combat swimmer.
Italy, Britain, the United States, and other nations developed specialized underwater units, although their missions and equipment differed considerably.
Some were designed primarily to attack ships in harbor. Others concentrated on reconnaissance and the demolition of underwater obstacles before amphibious assaults.
The common feature was the same: the diver could enter an area without using the normal approaches available to conventional forces.
Italian Frogmen
The Italian Decima MAS became particularly well known for its attacks against Allied shipping.
Its operators used Maiali, or human torpedoes, to transport divers toward defended harbors. The divers could then leave the vehicle, approach their targets, and attach explosive charges before withdrawing.
The most famous operation occurred at Alexandria, Egypt, on December 19, 1941.
Italian frogmen entered the British naval base and placed explosive charges against the battleships HMS Queen Elizabeth and HMS Valiant, as well as other vessels.
Both battleships were seriously damaged.
The raid demonstrated the strategic potential of combat diving. A handful of men, operating almost entirely beneath the surface, had managed to penetrate a major naval base and put two capital ships out of action.
It was a remarkable demonstration of what would become a recurring principle in special operations: the size of the attacking force mattered less when the force could bypass the defenses entirely.
American Underwater Demolition Teams
The American approach developed along somewhat different lines.
The U.S. Navy created Underwater Demolition Teams, or UDTs, during World War II in response to the difficulties encountered during amphibious operations.
At Tarawa in 1943, landing craft encountered an unexpectedly extensive coral reef, contributing to heavy casualties. The experience demonstrated the importance of sending specialized swimmers ahead of an amphibious assault to examine beaches and clear underwater obstacles.
The UDTs that emerged from this effort became specialists in underwater reconnaissance and demolition.
Their first combat mission occurred at Saipan in June 1944. UDT personnel subsequently participated in amphibious operations throughout the Pacific. During preparations for Okinawa, one team removed approximately 1,200 underwater obstacles in two days.
Their work was dangerous precisely because it had to be conducted close to defended beaches. The swimmers were required to survey the approaches, locate obstacles, and clear landing routes while exposed to enemy observation and fire.
There is also an important distinction between these wartime UDTs and the modern image of a scuba-equipped frogman.
The UDTs did not generally conduct their operations using modern scuba equipment.
The Navy experimented with several breathing systems, but suitable scuba equipment was not readily available during the war (Mainly due to material shortage). Open-circuit Aqua-Lung equipment did not become important to UDT operations until after the war.
Much of the famous American underwater demolition work was therefore performed by swimmers operating on breath-hold.
Christian Lambertsen and American Combat Swimming
One of the most important figures in the development of American military diving was Dr. Christian Lambertsen.
While still a medical student, Lambertsen developed the Lambertsen Amphibious Respiratory Unit, or LARU, a closed-circuit breathing apparatus.
The device recycled the diver's exhaled air rather than releasing it into the surrounding water. This allowed the swimmer to remain underwater without the conspicuous trail of bubbles produced by conventional scuba.
The Office of Strategic Services recognized its potential for clandestine operations, and Lambertsen became involved with the OSS Maritime Unit. He trained operational swimmers in underwater infiltration, reconnaissance, and demolition.
The significance of Lambertsen's work extends beyond the equipment itself. His research helped establish the scientific foundation of American combat swimming, particularly in areas such as oxygen toxicity, carbon-dioxide accumulation, and the physiological limits of prolonged underwater operations.
His work would influence military diving for decades.
The Postwar Resurgence of Scuba
After 1945, diving entered a new period.
The development of the Aqua-Lung, associated with Jacques-Yves Cousteau and Émile Gagnan, made open-circuit scuba practical on a much broader scale.
The U.S. Navy acquired Aqua-Lung equipment in 1947, and UDT personnel began experimenting with its military applications.
The advantages were considerable. Divers were no longer dependent on a surface vessel for their breathing supply and could operate independently over a much greater area.
There was, however, an obvious drawback.
Open-circuit scuba produced bubbles.
Consequently, military diving developed around two complementary technologies. Open-circuit scuba was useful for many engineering, salvage, reconnaissance, and demolition tasks, while closed-circuit systems remained particularly valuable for covert operations where concealment was essential.
The postwar period was therefore not simply the "invention of military scuba." It was the point at which several different forms of underwater breathing became specialized for different military purposes.
Korea
The Korean War provided the next major test of American combat diving.
UDTs conducted reconnaissance, demolition, mine-related operations, and coastal missions. They also conducted operations against infrastructure and maritime targets.
During the war, the UDTs increasingly demonstrated that their usefulness extended beyond preparing beaches for amphibious assaults. They could conduct reconnaissance and demolition missions independently, operate in rivers and coastal areas, and support broader special operations.
The Navy's own history describes the destruction of an entire port complex by UDT personnel during the strategic withdrawal from Korea.
The role of the combat swimmer was consequently beginning to change.
The diver was becoming less of an engineer who happened to operate underwater and more of a specialized operator whose ability to use the water gave him access to otherwise inaccessible targets.
The Cold War
The Cold War gave military diving an entirely new strategic importance.
The United States and Soviet Union possessed enormous naval forces, submarine fleets, naval bases, and coastal installations. At the same time, both sides invested heavily in special operations and clandestine reconnaissance.
Underwater infiltration offered an attractive solution.
A submarine could transport personnel toward an enemy coastline. Combat swimmers could then leave the submarine and approach their objective beneath the surface, potentially avoiding conventional coastal defenses.
The development of Swimmer Delivery Vehicles, or SDVs, extended this concept even further. Instead of requiring combat swimmers to cover long distances under their own power, small submersible vehicles could transport them toward the target.
The basic concept became:
Submarine → underwater vehicle → combat swimmers → objective.
The technology transformed diving from a method of swimming underwater into an entire system of covert mobility.
The Creation of the SEALs
The evolution of the UDTs eventually produced the modern American naval special-operations community.
In January 1962, the U.S. Navy established SEAL Teams ONE and TWO.
The name, standing for Sea, Air, Land, reflected the broader mission of the new organization. The SEALs inherited the maritime skills and traditions of the UDTs but were intended to conduct unconventional warfare and clandestine operations across multiple environments.
Combat diving therefore became one capability within a much larger special-operations system.
A SEAL might use scuba or a rebreather to enter an area, but the ultimate mission could involve reconnaissance, intelligence collection, demolition, direct action, or operations entirely on land.
The diving equipment was a means of gaining access.
Vietnam
Vietnam further demonstrated this evolution.
The country's extensive rivers, canals, swamps, and coastline provided an environment in which maritime mobility was central to military operations.
SEALs and UDT personnel conducted river and coastal reconnaissance, demolition, canal clearance, and counterinsurgency operations. SEALs began conducting direct-action missions in Vietnam in 1966, eventually maintaining a substantial presence there.
The conflict demonstrated that military diving did not require an obvious naval target.
Water itself could serve as a route of infiltration.
A river could become a concealed avenue of approach. A canal could provide access behind enemy positions. A coastline could provide an alternative route around conventional defenses.
The Mature Cold War Diver
By the 1970s and 1980s, military diving had become an increasingly sophisticated field.
A combat swimmer could employ:
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Closed-circuit rebreathers for covert movement
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Open-circuit scuba for other underwater tasks
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Specialized navigation equipment
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Underwater propulsion
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Swimmer Delivery Vehicles
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Demolition equipment
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Waterproof communications and instrumentation
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Submarine-based deployment
At the same time, underwater medicine had become an important scientific discipline. Understanding oxygen toxicity, decompression, carbon-dioxide accumulation, and the effects of pressure was essential to allowing divers to operate deeper and for longer periods.
The military diver of the late Cold War was therefore the product of several disciplines coming together: engineering, physiology, naval warfare, special operations, and underwater navigation.
Modern Military Diving
The end of the Cold War did not make combat diving obsolete.
Instead, its applications became more specialized.
Modern military divers can be divided broadly into several categories.
Special Operations
Combat swimmers continue to provide a means of covert maritime infiltration, reconnaissance, and other special operations.
Explosive Ordnance Disposal
Military divers locate and neutralize mines, unexploded ordnance, and other underwater hazards.
Salvage and Rescue
Divers remain essential for recovering personnel, aircraft, ships, and equipment.
Construction and Engineering
Military diving units conduct underwater construction, repair, inspection, and maintenance.
Maritime Security
Divers can inspect ships, piers, harbors, and other underwater structures for explosives or other hazards.
The U.S. Navy's diving community today encompasses all of these functions, rather than treating "military diver" as synonymous with special operations.
The Seabed as a Battlefield
The nature of underwater warfare is changing once again.
Modern societies depend heavily on infrastructure beneath the sea, including telecommunications cables, pipelines, energy installations, sensors, and other systems.
This has expanded the strategic importance of the seabed itself.
The military significance of diving is consequently no longer limited to attacking ships or clearing beaches. Underwater forces can be used for reconnaissance and inspection of infrastructure, protection of naval installations, and access to locations that are difficult to approach from the surface.
In this respect, modern military diving has returned to one of its oldest principles: the underwater environment provides access to places that are difficult to reach by conventional means.
Conclusion
The history of military diving is unusually continuous.
The ancient diver and the modern combat swimmer are separated by thousands of years of technological development, yet the underlying military logic remains remarkably similar.
Ancient divers exploited the blind spot beneath an enemy vessel. Nineteenth-century divers extended the duration of underwater operations through surface-supplied air. The First World War revived underwater sabotage, while the Second World War produced the first mature generation of combat swimmers and frogmen.
The postwar development of scuba made independent underwater movement considerably more practical. Closed-circuit rebreathers solved a different problem: concealment. During the Cold War, these technologies were combined with submarines, specialized navigation, and underwater delivery vehicles, eventually becoming part of the capabilities of modern special-operations forces.
Today, military diving encompasses far more than the classic image of the frogman.
It is simultaneously a discipline of engineering, reconnaissance, demolition, salvage, special operations, and maritime security.
The essential advantage, however, has remained unchanged since antiquity.
A military force that can move beneath the surface possesses an avenue of approach that its opponent may not be prepared to defend.
And that is why, despite the enormous technological changes of modern warfare, the military diver has never entirely disappeared. Nothing is more concealing than the deep void of the ocean waves, nor is anything more suffocating. If a nation can brave the depths of the aquatic beast, it can tame its waves and turn the tide in its favor. Or Die Trying.