The diving equipment developed by Charles and John Deane, Augustus Siebe, and
other inventors gave man the ability to remain and work underwater for extended
periods, but movement was greatly limited by the requirement for surfacesupplied
air. Inventors searched for methods to increase the diver’s movementwithout increasing the hazards. The best solution was to provide the diver with a
portable, self-contained air supply. For many years the self-contained underwater
breathing apparatus (scuba) was only a theoretical possibility. Early attempts to
supply self-contained compressed air to divers were not successful due to the limitations
of air pumps and containers to compress and store air at sufficiently high
pressure. Scuba development took place gradually, however, evolving into three
Open-circuit scuba (where the exhaust is vented directly to the surrounding
Closed-circuit scuba (where the oxygen is filtered and recirculated), and
- Semiclosed-circuit scuba (which combines features of the open- and closedcircuit
In the open-circuit apparatus, air is inhaled from a supply
cylinder and the exhaust is vented directly to the surrounding water.
The first and highly necessary component of
an open-circuit apparatus was a demand regulator. Designed early in 1866 and
patented by Benoist Rouquayrol, the regulator adjusted the flow of air from the
tank to meet the diver’s breathing and pressure requirements. However, because
cylinders strong enough to contain air at high pressure could not be built at the
time, Rouquayrol adapted his regulator to surface-supplied diving equipment and
the technology turned toward closed-circuit designs. The application of
Rouquayrol’s concept of a demand regulator to a successful open-circuit scuba
was to wait more than 60 years.
The thread of open-circuit development
was picked up in 1933. Commander LePrieur, a French naval officer, constructed
an open-circuit scuba using a tank of compressed air. However, LePrieur did not
include a demand regulator in his design and, the diver’s main effort was divertedto the constant manual control of his air supply. The lack of a demand regulator,
coupled with extremely short endurance, severely limited the practical use of
At the same time that actual combat operations
were being carried out with closed-circuit apparatus, two Frenchmen
achieved a significant breakthrough in open-circuit scuba design. Working in a
small Mediterranean village, under the difficult and restrictive conditions of
German-occupied France, Jacques-Yves Cousteau and Emile Gagnan combined an
improved demand regulator with high-pressure air tanks to create the first truly
efficient and safe open-circuit scuba, known as the Aqua-Lung. Cousteau and his
companions brought the Aqua-Lung to a high state of development as they
explored and photographed wrecks, developing new diving techniques and testing
The Aqua-Lung was the culmination of hundreds of years of progress, blending
the work of Rouquayol, LePrieur, and Fleuss, a pioneer in closed-circuit scuba
development. Cousteau used his gear successfully to 180 fsw without significant
difficulty and with the end of the war the Aqua-Lung quickly became a commercial
success. Today the Aqua-Lung is the most widely used diving equipment,
opening the underwater world to anyone with suitable training and the fundamental
The underwater freedom brought about by the development
of scuba led to a rapid growth of interest in diving. Sport diving has
become very popular, but science and commerce have also benefited. Biologists,
geologists and archaeologists have all gone underwater, seeking new clues to the
origins and behavior of the earth, man and civilization as a whole. An entire
industry has grown around commercial diving, with the major portion of activity
in offshore petroleum production.
After World War II, the art and science of diving progressed rapidly, with
emphasis placed on improving existing diving techniques, creating new methods,
and developing the equipment required to serve these methods. A complete generation
of new and sophisticated equipment took form, with substantial
improvements being made in both open and closed-circuit apparatus. However,
the most significant aspect of this technological expansion has been the closely
linked development of saturation diving techniques and deep diving systems.
The basic closed-circuit system, or oxygen rebreather, uses
a cylinder of 100 percent oxygen that supplies a breathing bag. The oxygen used
by the diver is recirculated in the apparatus, passing through a chemical filter that
removes carbon dioxide. Oxygen is added from the tank to replace that consumed
in breathing. For special warfare operations, the closed-circuit system has a major
advantage over the open-circuit type: it does not produce a telltale trail of bubbles
on the surface.
Henry A. Fleuss developed the first commercially
practical closed-circuit scuba between 1876 and 1878 (Figure 1-9). The Fleuss device consisted of a watertight rubber face mask and a breathing bag connected
to a copper tank of 100 percent oxygen charged to 450 psi. By using oxygen
instead of compressed air as the breathing medium, Fleuss eliminated the need for
high-strength tanks. In early models of this apparatus, the diver controlled the
makeup feed of fresh oxygen with a hand valve.
Fleuss successfully tested his apparatus in 1879. In the
first test, he remained in a tank of water for about an
hour. In the second test, he walked along a creek bed at
a depth of 18 feet. During the second test, Fleuss turned
off his oxygen feed to see what would happen. He was
soon unconscious, and suffered gas embolism as his
tenders pulled him to the surface. A few weeks after his
recovery, Fleuss made arrangements to put his recirculating
design into commercial production.
In 1880, the Fleuss scuba figured prominently in a
highly publicized achievement by an English diver,
Alexander Lambert. A tunnel under the Severn River
flooded and Lambert, wearing a Fleuss apparatus,
walked 1,000 feet along the tunnel, in complete darkness,
to close several crucial valves.
Figure 1-9. Fleuss
As development of
the closed-circuit design continued, the Fleuss equipment
was improved by adding a demand regulator and
tanks capable of holding oxygen at more than 2,000
psi. By World War I, the Fleuss scuba (with modifications)
was the basis for submarine escape equipment
used in the Royal Navy. In World War II, closed-circuit
units were widely used for combat diving operations
(see paragraph 1-3.5.2).
Some modern closed-circuit systems employ a mixed gas for breathing and electronically
senses and controls oxygen concentration. This type of apparatus retains
the bubble-free characteristics of 100-percent oxygen recirculators while significantly
improving depth capability.
Fleuss had been unaware of the serious
problem of oxygen toxicity caused by breathing 100 percent oxygen under pressure.
Oxygen toxicity apparently was not encountered when he used his apparatus
in early shallow water experiments. The danger of oxygen poisoning had actually
been discovered prior to 1878 by Paul Bert, the physiologist who first proposed
controlled decompression as a way to avoid the bends. In laboratory experiments
with animals, Bert demonstrated that breathing oxygen under pressure could lead
to convulsions and death (central nervous system oxygen toxicity).
In 1899, J. Lorrain Smith found that breathing oxygen over prolonged periods of
time, even at pressures not sufficient to cause convulsions, could lead to pulmonary
oxygen toxicity, a serious lung irritation. The results of these experiments,
however, were not widely publicized. For many years, working divers were
unaware of the dangers of oxygen poisoning.
The true seriousness of the problem was not apparent until large numbers of
combat swimmers were being trained in the early years of World War II. After a
number of oxygen toxicity accidents, the British established an operational depth
limit of 33 fsw. Additional research on oxygen toxicity continued in the U.S. Navy
after the war and resulted in the setting of a normal working limit of 25 fsw for 75
minutes for the Emerson oxygen rebreather. A maximum emergency depth/time
limit of 40 fsw for 10 minutes was also allowed.
These limits eventually proved operationally restrictive, and prompted the Navy
Experimental Diving Unit to reexamine the entire problem of oxygen toxicity in
the mid-1980s. As a result of this work, more liberal and flexible limits were
adopted for U.S. Navy use.
True scientific impetus was first given to the saturation
concept in 1957 when a Navy diving medical officer, Captain George F.
Bond, theorized that the tissues of the body would eventually become saturated
with inert gas if exposure time was long enough. Bond, then a commander and the
director of the Submarine Medical Center at New London, Connecticut, met with
Captain Jacques-Yves Cousteau and determined that the data required to prove the
theory of saturation diving could be developed at the Medical Center.
The semiclosed-circuit scuba combines features of
the open and closed-circuit systems. Using a mixture of gases for breathing, the
apparatus recycles the gas through a carbon dioxide removal canister and continually
adds a small amount of oxygen-rich mixed gas to the system from a supply
cylinder. The supply gas flow is preset to satisfy the body’s oxygen demand; an
equal amount of the recirculating mixed-gas stream is continually exhausted to the
water. Because the quantity of makeup gas is constant regardless of depth, the
semiclosed-circuit scuba provides significantly greater endurance than opencircuit
systems in deep diving.
In the late 1940s, Dr. C.J. Lambertsen
proposed that mixtures of nitrogen or helium with an elevated oxygen content be
used in scuba to expand the depth range beyond that allowed by 100-percent
oxygen rebreathers, while simultaneously minimizing the requirement for
In the early 1950s, Lambertsen introduced the FLATUS I, a semiclosed-circuit
scuba that continually added a small volume of mixed gas, rather than pure
oxygen, to a rebreathing circuit. The small volume of new gas provided the
oxygen necessary for metabolic consumption while exhaled carbon dioxide was
absorbed in an absorbent canister. Because inert gas, as well as oxygen, was added
to the rig, and because the inert gas was not consumed by the diver, a small
amount of gas mixture was continuously exhausted from the rig.
In 1964, after significant development work, the Navy adopted a
semiclosed-circuit, mixed-gas rebreather, the MK 6 UBA, for combat swimming
and EOD operations. Decompression procedures for both nitrogen-oxygen and
helium-oxygen mixtures were developed at the Navy Experimental Diving Unit.
The apparatus had a maximum depth capability of 200 fsw and a maximum endurance
of 3 hours depending on water temperature and diver activity. Because the apparatus was based on a constant mass flow of mixed gas, the endurance was
independent of the diver’s depth.
In the late 1960s, work began on a new type of mixed-gas rebreather technology,
which was later used in the MK 15 and MK 16 UBAs. In this UBA, the oxygen
partial pressure was controlled at a constant value by an oxygen sensing and addition
system. As the diver consumed oxygen, an oxygen sensor detected the fall in
oxygen partial pressure and signaled an oxygen valve to open, allowing a small
amount of pure oxygen to be admitted to the breathing circuit from a cylinder.
Oxygen addition was thus exactly matched to metabolic consumption. Exhaled
carbon dioxide was absorbed in an absorption canister. The system had the endurance
and completely closed-circuit characteristics of an oxygen rebreather without
the concerns and limitations associated with oxygen toxicity.
Beginning in 1979, the MK 6 semiclosed-circuit underwater breathing apparatus
(UBA) was phased out by the MK 15 closed-circuit, constant oxygen partial pressure
UBA. The Navy Experimental Diving Unit developed decompression
procedures for the MK 15 with nitrogen and helium in the early 1980s. In 1985, an
improved low magnetic signature version of the MK 15, the MK 16, was approved
for Explosive Ordnance Disposal (EOD) team use.
Although closed-circuit equipment was restricted
to shallow-water use and carried with it the potential danger of oxygen
toxicity, its design had reached a suitably high level of efficiency by World War II.
During the war, combat swimmer breathing units were widely used by navies on
both sides of the conflict. The swimmers used various modes of underwater attack.
Many notable successes were achieved including the sinking of several battleships,
cruisers, and merchant ships.
using closed-circuit gear, rode chariot torpedoes
fitted with seats and manual controls in
repeated attacks against British ships. In
1936, the Italian Navy tested a chariot torpedo
system in which the divers used a descendant
of the Fleuss scuba. This was the
Davis Lung (Figure 1-10). It was originally
designed as a submarine escape device and
was later manufactured in Italy under a license
from the English patent holders.
British divers, carried to the scene of action
in midget submarines, aided in placing
explosive charges under the keel of the
German battleship Tirpitz. The British began
their chariot program in 1942 using the
Davis Lung and exposure suits. Swimmers
using the MK 1 chariot dress quickly discovered that the steel oxygen bottles adversely affected the compass of the chariot
torpedo. Aluminum oxygen cylinders were not readily available in England, but
German aircraft used aluminum oxygen cylinders that were almost the same size
as the steel cylinders aboard the chariot torpedo. Enough aluminum cylinders were
salvaged from downed enemy bombers to supply the British forces.
Changes introduced in the MK 2 and MK 3 diving dress involved improvements
in valving, faceplate design, and arrangement of components. After the war, the
MK 3 became the standard Royal Navy shallow water diving dress. The MK 4
dress was used near the end of the war. Unlike the MK 3, the MK 4 could be
supplied with oxygen from a self-contained bottle or from a larger cylinder carried
in the chariot. This gave the swimmer greater endurance, yet preserved freedom of
movement independent of the chariot torpedo.
In the final stages of the war, the Japanese employed an underwater equivalent of
their kamikaze aerial attack—the kaiten diver-guided torpedo.
Figure 1-10. Original Davis
Submerged Escape Apparatus.
There were two groups of U.S. combat swimmers
during World War II: Naval beach reconnaissance swimmers and U.S. operational
swimmers. Naval beach reconnaissance units did not normally use any breathing
devices, although several models existed.
U.S. operational swimmers, however,
under the Office of Strategic Services,
developed and applied advanced methods
for true self-contained diver-submersible
operations. They employed the
Lambertsen Amphibious Respiratory
Unit (LARU), a rebreather invented by
Dr. C.J. Lambertsen (see Figure 1-11).
The LARU was a closed-circuit oxygen
UBA used in special warfare operations
where a complete absence of exhaust
bubbles was required. Following World
War II, the Emerson-Lambertsen Oxygen
Rebreather replaced the LARU (Figure
1-12). The Emerson Unit was used extensively
by Navy special warfare divers
until 1982, when it was replaced by the
Draeger Lung Automatic Regenerator
(LAR) V. The LAR V is the standard unit
now used by U.S. Navy combat swimmers
(see Figure 1-13).
Today Navy combat swimmers are organized into two separate groups, each with
specialized training and missions. The Explosive Ordnance Disposal (EOD) team
handles, defuses, and disposes of munitions and other explosives. The Sea, Air
and Land (SEAL) special warfare teams make up the second group of Navy combat swimmers. SEAL team members are trained to operate in all of these environments.
They qualify as parachutists, learn to handle a range of weapons,
receive intensive training in hand-to-hand combat, and are expert in scuba and
other swimming and diving techniques. In Vietnam, SEALs were deployed in
special counter-insurgency and guerrilla warfare operations. The SEALs also
participated in the space program by securing flotation collars to returned space
capsules and assisting astronauts during the helicopter pickup.
Figure 1-11. Lambertsen Amphibious
Respiratory Unit (LARU)
Figure 1-12. Emerson-Lambertsen
Figure 1-13. Draeger LAR V UBA.
The Navy’s Underwater Demolition Teams (UDTs) were
created when bomb disposal experts and Seabees (combat engineers) teamed
together in 1943 to devise methods for removing obstacles that the Germans were
placing off the beaches of France. The first UDT combat mission was a daylight
reconnaissance and demolition project off the beaches of Saipan in June 1944. In
March of 1945, preparing for the invasion of Okinawa, one underwater demolition
team achieved the exceptional record of removing 1,200 underwater obstacles in 2
days, under heavy fire, without a single casualty.
Because suitable equipment was not readily available, diving apparatus was not
extensively used by the UDT during the war. UDT experimented with a modified
Momsen lung and other types of breathing apparatus, but not until 1947 did the
Navy’s acquisition of Aqua-Lung equipment give impetus to the diving aspect of
UDT operations. The trail of bubbles from the open-circuit apparatus limited the
type of mission in which it could be employed, but a special scuba platoon of UDT
members was formed to test the equipment and determine appropriate uses for it.
Through the years since, the mission and importance of the UDT has grown. In the
Korean Conflict, during the period of strategic withdrawal, the UDT destroyed anentire port complex to keep it from the enemy. The UDTs have since been incorporated
into the Navy Seal Teams.