One of the best and best known diving helmets in the world is the US Navy Mark V. Until about 1912 there was hardly any serious (deep) diving activity in the US Navy. Commercial Morse and Schrader helmets were used. US Navy gunner George D. Stillson wrote a letter to the Bureau of Construction and Repair (now the Bureau of Ships) in which he complained about the Navy's equipment and diving techniques. He suggested to check the practicability of Haldane's stage method of decompression and to improve the standard Navy diving gear to permit deeper dives. The Bureau gave Stillson the assignment. It took several years and the help of a team of military and commercial diving experts to complete the heavy task. The design of the new diving helmet was based on commercial Morse and Schrader helmets of that time and the team also tested Siebe and Draeger equipment. Extensive tests were conducted in diving tanks ashore and later from the U.S.S. Walke in Long Island Sound. In 1915 Stillson reported to the bureau in the Report on Deep diving tests. It contained drawings and descriptions of the precursor of the MkV and of a lot of other navy diving equipment. Stillson layed the foundations for professional diving in the US Navy.

The helmet had a top view port to provide the diver with an upward view. The front view port, called the faceplate, was hinged. Like this, no tender could incidently drop a faceplate overboard ! On the commercial helmets they tested, the exhaust was at the rear of the helmet. This was a good spot: air bubbles would not block the divers' view. However, it was sometimes hard to operate the handle at the back of the helmet. So, the exhaust was moved to the right front side of the helmet and an external "banana" tube was applied to exhaust the air at the rear of the bonnet. Conventional 3 light helmets had air channels to prevent the windows from steaming up. On a 4 light helmet this was a bit of a problem: 2 side view ports and the top view port got an airchannel. A spitcock was put on the bonnet between the faceplate and the left view port so the diver could suck in some water and spit it against the inside of the faceplate in case it would steam up. The spitcock could also be used to "fine tune" the buoyancy.

Commercial 4 light Morse helmet from around 1915. This hat is a direct precursor of the Mark V.  
It looks like the spitcock and the "sacrificial zinc" (an anti-electrolysis agent used to retard corrosion) have been removed. 
The hat has the typical view ports and hinged faceplate. The corselet features two nipples for weights. 
There is no banana-exhaust. On the rectangular nametag it says:

The Mark V was used by the US Navy from 1916 till 1984, when the fiber glass Mark XII that was introduced in 1979, finally took over permanently. As we stated, only some minor changes were made to MkV in that period. Next to the Navy, a lot of commercial divers used (and still use !) the Mark V as well. Besides this the helmet is used by many Working Equipment Groups (WEG) including DWEG for fun, education and demonstration and thus to keep the memory of this great helmet alive.

The following companies produced the Mark V:

The very first MkV appeared in the 1916 US Navy Diving Manual. It was a Morse. The oldest MkV helmet known in The World is a 1916 Morse Mark V helmet which is serial number 2204. It belongs to John Durham of Durham Diving Services

The helmet on the right is a 1918 Schrader, the one on the left is a Schrader that dates from 1943. The only visible difference between them is the eight point exhaust handle that you only find on hats from 1918 and older. It was changed to a four point handle on divers' requests. It allowed the diver to more easily adjust the valve and determine its setting. The other main difference worth mentioning here is that the World War 1 I breastplates were narrower and not as heavy as World War 2 ones. Pictures contributed by one of our viewers who would like to stay anonymous.

Since there are hardly any helmets left on the free market but there still is a demand, Morse and Desco produce new helmets on customers demand, according to US Navy specifications.

An absolute new Schrader hat from 1918.
Notice the eight point exhaust handle that you only find on hats produced during or prior to 1918.

Photo Courtesy West Sea Co.

A tinned Schrader MARK V from the WW II era. 
Tin was used to prevent corrosion caused by sea water.

Photo Courtesy West Sea Co.

A close examination

Lets have a closer look at all the Mark V components. We will use a June 1942 Schrader hat with matching numbers 303A for this exercise. What we discuss goes for Morse, Desco and Miller Dunn MKV helmets also. There are only some very slight differences in the exact location of components from different manufacturers (like the exact position of the studs) and the rounding of the corselet. 

The bonnet

Consists of a spun copper dome with four heat-treated, sealed glass viewports. On the back of the helmet you find two elbows. The one on the left is the air inlet elbow, the one on the right is called the telephone gooseneck.

Inside the bonnet you will find two small threaded machine screws that are soldered into the phone box to hold the reproducer, while several half inch brass taps are situated within the bonnet to hold the phone cable leading from the gooseneck to the phone box.

There are three flat distribution ducts to spray the supply air over the viewports to prevent fogging.


At the bottom, the bonnet has an interrupted threaded ring that screws into the interrupted threaded ring on the breastplate.

The bonnet is actually lowered in place about one-eight of a turn out of alignment, due to the interrupted thread on bonnet and breastplate. Then, while one tender holds the breastplate, the other one twists the bonnet into place. The mating threads engage to thrive the bonnet down tightly on the leather neckring gasket; this forms a watertight seal.

Bonnet and breastplate have a marking on the front. When these two markings are in line, the bonnet is placed exactly right.

The viewports

All four viewports are guarded with protective brass grills. The glass is about 0.3 " thick.

In 1971 the US Navy changed the specifications from glass to acrylic windows for safety. (now you know how it is possible that you encountered a hat with "plastic" windows !)

The faceplate

The front viewport is called faceplate. It is the only one that can be opened. This way the diver can speak to the tender without removing the bonnet. The faceplate on the Mark V is hinged, which is quite unique for diving helmets. The Danish Hanssen has this same feature. Practically all other helmets have a "screw in" faceplate. A wingnut on a pivoting stud extending from the bonnet is rounded and tapered on the "seating" end and fits precisely into the receiving cup of the two pronged fork on the faceplate. To prevent the wingnut from unscrewing completely a small circular "keeper" is swaged onto the end of the stud.

The non return valve

The most important safety device on the helmet is screwed onto the air inlet gooseneck on the back of the bonnet. The other end of the non return valve is screwed into the whip. Its purpose is to prevent the diver from being injured by "squeeze" in the event that the air hose bursts, or the air supply system becomes so seriously damaged as to fail to maintain an air pressure sufficient to counteract the external water pressure. The pressure inside the dress and the helmet would get below the pressure of the surrounding water and the divers’ body would be squeezed into the helmet. The valve sometimes carries the helmet manufacturers name and, in case of Navy use, the US Navy inspectors stamp. Needles to say the valve has to function properly at all times.

The exhaust valve

Is positioned to the lower right side of the faceplate. It is a spring loaded valve that controls the amount of air inside the diver’s outfit. Two springs are inside it. One will open when the pressure inside the helmet rises to ½ pound per square inch; and by means of a hand wheel on the outside the diver can regulate the amount of air passing out of the valve. It allows the diver to maintain sufficient air pressure inside the dress to avoid a squeeze and it helps him controlling his buoyancy. The second spring acts to guard against an over-pressure inside the suit. If the air pressure inside the dress were to exceed the outside water pressure by about two pounds per square inch, several serious accidents could result. Think about a blowup or when the pressure gets to high it causes the dress to tear and the diver to drown.

The exhaust hand wheel

On helmets manufactured prior to about 1918, an eight point exhaust handle was used. After that, on divers’ request, the exhaust only had a four point handle featuring an enlarged bulb on one of the prongs for reference. Most of these new style handles were manufactured by the Batteryless Telegraph Equipment company whose logo, BTE, was cast into the center. Frequently the helmet manufacturer’s name was lightly impressed on the circumference on the exhaust valve cover bracket, just behind the valve handle.

Chin button

The exhaust valve has a manual control on the inside of the helmet. It is mushroom-shaped and is called the "chin button". By pushing this button with the chin, the diver can open the valve all the way, thus overriding both valve springs, and allowing maximum airflow out of the helmet. This button may also be grasped with the lips and pulled inward to seal the valve closed, thus allowing no air to escape from the helmet.

Banana exhaust

After the air passes through the exhaust valve, it is channeled along the outside of the helmet, under the right side viewport, and exhausts at the rear. This feature keeps the air bubbles from rising across the viewports and faceplate.

Transciever recess

Positioned on the left front on top of the bonnet. It holds the divers’ transceiver. On helmets used in naval service, The US Navy’s inspector’s mark -- the initials US with a small anchor between – are stamped into it.


Located to the lower left of the faceplate. It was originally designed for taking water samples. However, it can also be used to exhaust air as a fine adjustment for buoyancy control or as the primary exhaust. Also, water may be intentionally drawn in through the spitcock to clear a fogged viewport or to soothe parched lips.

Dumb-bell lock

To ensure that the bonnet is affixed to the breastplate in the centered, working position, a safety pin or dump-bell lock is employed. The dumb-bell is pivoted of the back of the bonnet and fits into a slot at the back of the breastplate. To prevent the dumb-bell from coming out of the slot a formed piece of brass, the dumb-bell lock retainer clip, is attached to the neckring. It pivotes on one end and is secured by means of a copper pin attached with a small chain on the other. In this case you see the old style retainer clip. It turned out to be very vulnerable and was later replaced with a more rugged design.

Brass plate

A rectangular brass plate situated above the spitcock between the facepalate and the viewport was used to attach a thin brass plate to hold the hinged brass faceplate in an open position.

The breastplate

Is shaped so that it fits comfortably over the shoulders, chest and back. The neck portion of the breastplate has a threaded ring that screws into the ring on the bonnet. The two eyelets on the front of the breastplate are used for securing the lifeline and air hose with a lanyard.

The Brales

Are made of solid brass. There are 4 brales that carry inscriptions like FRONT and BACK and, in many cases, carry the helmet number as well. Morse numbered the brales on the topside, Schrader did so underneath. Notice that the brales are solid and not hollow.

Studs, nuts and washers

The helmet has 12 equally spaced studs that are positioned on the edge of the breastplate. The stud on the left front side is called the bastard stud. It is longer than the others because it holds the air control valve.

Copper washers are placed under the brales at the junction to assist in making a seal at these points. 12 wingnuts are used to secure the brales to the breastplate, flanged ones being used at the junction of the brales.


The whip

Is a 3 feet air hose that is connected to the non-return valve with one end and to the air control valve with the other end.

The air control valve

The air that reaches the diver normally comes from a compressor or a high pressure storage on the surface. By turning the handle, the diver operates a needle-valve that controls the amount of air flowing into the helmet. It features a link and eye pad, used to connect the valve to the bastard stud on the left front side of the breastplate. One end of the air control valve is connected to the air hose coming from the surface, the other one to the whip.

See the MkV diver coming up!!


  • Last edited on 13th May 2012