At the start of WW II, two companies were manufacturing the MK V Deep Sea Diving helmet – Morse and Schrader, but after the attack on Pearl Harbor in December of 1941, DESCO and Miller-Dunn also began manufacturing the MK V.
Although heavy and cumbersome by modern standards, the MK V provided the diver with a safe working environment, protecting him from not only the cold but also pollutants and infections. It also had adequate communications and a built-in air reserve, so it is not surprising that the MK V served with distinction and survived in the navy dive lockers until the mid-eighties, to be replaced by the more advanced lightweight MK 12.

“Jack Browne” & MK 20
In the forties, as a lightweight alternative to the MK V, the navy went to a triangular-shaped mask named after its inventor “Jack Browne”, which had a normal depth limit of 60 feet and a maximum of 90 feet. This simple mask was in service right up into the late seventies and early eighties, however this was a free-flow mask and did not support a voice communications system. Communications were effected by a series of line-pull signals on the umbilical to the topside tender.
The current lightweight diving mask used by navy divers is the MK 20 Aga mask, which has two-way communications and a normal working depth limit for the navy of 60 feet. These lightweight masks have a low profile so are well suited to work in confined spaces such as those found in submarine husbandry work.

MK-1 Mod 0
In 1976 the Navy approved the Kirby-Morgan Bandmask, designated the US Navy Mask MK-1 Mod 0, for use as a lightweight diving mask. The MK-1 could be used to 60 feet without a come-home bottle, 130 feet with a come-home emergency bailout bottle, and 190 feet with an open bell. The MK-1 Mod 0 Lightweight, Mixed-Gas Diving Outfit was also approved for dives to 300 fsw on helium-oxygen.

By the late seventies, the MK V was still in use by navy divers giving them a normal working limit on air to 190 feet or down to 250 feet for 90 minutes on Exceptional Exposure diving operations. However, in ’78 and ’79 NEDU was developing four new systems; the Mark 11 semi-closed circuit system; the Mark 14 “push/pull” to conserve helium and extend dive times on saturation dives; the MK 15 UBA mixed gas rebreather; and the MK 12 SSDS.

MK 12 SSDS
The MK 12 Surface-Supported Diving System (SSDS) came onto the scene in the late seventies and by 1980 had replaced the heavy MK V Mod 1 gas hat for deep mixed-gas diving. Then in 1985 the MK 12 was officially approved for all Fleet diving to replace the standard MK V heavy gear, marking the death of a “heavy metal” era in navy diving.
The MK 12 SSDS was very much a “system” approach to diving with several integrated components. In addition to the helmet assembly, consisting of a shell and base, the dress assembly comprised of a dry suit, out garment, jocking harness, weights, lightweight boots, and gloves. Support equipment included the umbilical, wielding shields, flow meter, test set and tools, spare parts, a repair kit and a re-circulator assembly for mixed-gas diving. A MK 12 diving package contained three helmets, three 200-foot umbilicals and three 600-foot umbilicals.
However, the MK 12 was not a very successful design making the MK-1 bandmask more efficient for both gas and bell diving. In 1990 the MK-1 Mod 0 bandmask was replaced by the MK 21, a helmet based on Kirby-Morgan’s DSI Superlite 17B. Then three years later, in 1993, the MK 12 was also replaced by the MK 21 for all air and gas diving applications. If this is not confusing enough, the navy also acquired the DSI Heliox 18 bandmask designating it the MK 22.
The only item of the MK 12 system that survives to this day in navy dive lockers is the blue outer garment with its distinctive gold strip. This suit makes excellent chafing gear and is valued by navy divers for its numerous pockets that will hold tools, nuts, bolts, shackles and extra weights.

MK 21 / SuperLite 17B
The MK 21, known in the commercial diving field as a Kirby-Morgan or DSI SuperLite 17B, is constructed with a fiberglass shell that is weighted for neutral buoyancy so does not require an uncomfortable jocking system to stop the helmet floating up on the diver. It also has a demand regulator, greatly improving gas efficiency and eliminating much of the noise and communication interference associated with free-flow helmets.
For working at night, the MK 21 can be fitted with lights, and a video camera can be added so that the diving supervisor and attending engineers can see exactly what the diver is working on.

As with all surface-supplied diving rigs, the MK 21 diver is connected to the surface by an umbilical that serves several functions. First and foremost, the umbilical carries air or gas to the diver, fed from either a compressor or storage cylinders. The second component of the umbilical is a “coms” line giving the diver clear two-way communications with the surface. Also included in the bundle is a pneumo-fathometer or pneumo hose that allows the console operator to monitor the divers depth. In addition to all these, the umbilical can have a hot water hose for the diver’s hot water suit, a video cable and a power cable for the helmet light.
For added safety and security, the umbilical is attached to a harness, which may also carry the diver’s emergency gas supply (EGS), commonly called a bailout or come-home bottle. The navy harness are constructed from exceptionally strong webbing, riveted together with stainless steel D rings as attachment points. The navy approved black Atlantic Diving Equipment harnesses are designated the Mk 20 harness with no bailout and the Mk 21 with bailout and integrated weight pockets.
The topside component of all surface-supplied diving systems is the diving manifold or control console. For the navy dive teams this is the MK 3 Lightweight Diving System Console, volume tank assembly and CHAOS air racks. This is connected together by interface umbilicals and supplied by an LP compressor. However, each type of diving operation has its own Mission Configuration Matrix dictating the equipment components required.
As with most commercial diving operations, navy dive teams will have a chamber on site anytime there is a possibility of decompression problems, particularly on deeper jobs. The small transportable chamber that the navy uses is called a TRCS – Transportable Recompression Chamber System. This breaks into a primary lock and a transfer lock for easy of deployment.

FLY AWAY DIVING SYSTEMS
The modern deep-sea dive teams such as Mobile Diving & Salvage Units (MDSU) and Underwater Construction Teams (UCT) are very much air-mobile, even referring to their teams as Air Dets or Detachments. To facilitate rapid deployment and ease of use, pre-packaged surface-support systems were developed and containerized. These modular systems are referred to as “Fly-Aways”, and come in a number of components and configuration, including:
Fly-Away Dive Lockers (FADL)
Fly-Away Diving Systems (FADS)
FADS MK III Air System
FADS MK III Mixed Gas System (FMGS)
Fly-Away Recompression Chambers (FARCC)

The Fly-Away Recompression Chamber (FARCC) is a 200 cubic foot, double lock, steel chamber that is depth rated to 225 fsw and US Navy Certified. Mounted on a life support skid (LSS) and weighing in at 13,400 pounds fully outfitted, it comes with its own diesel generator, high-pressure air compressor and external conditioning system.
EOD has a modular diving system designated the MK 1 Mod 0 Mobile Support Facility comprised of one FARCC / LSS and one FADL.

As can be seen though-out this website, the yellow MK 21 diving helmet, with its distinctive kidney-shaped face-plate, is the signature piece of equipment for all navy deep-sea divers today, just as the MK V was for their predecessors. The MK 20 mask is the lightweight alternative for surface-supplied diving.
Not to be forgotten, it is still a source of considerable pride for a navy diver to be able to claim that he had been trained on the venerable MK V heavy gear. Unfortunately, the navy no longer dives the MK V so the polished helmets and dusty suited “Jakes” now adorn the offices and hallways of virtually every diving command in the navy. They stand as silent testament to a long history of courage and hard work, and a reminder to new divers of the proud traditions they must follow.