The idea of a rigid helmet and closed flexible dress dates back to Augustus Siebe in England in 1831, and by the Turn of the Century (1900) helmet diving on compressed air had become a fairly well-developed art with a variety of commercial equipment manufacturers around the world. The helmets generally followed Siebe's concept of a breastplate and three-light bonnet (the windows are known as "lights") with an interrupted-thread locking neck ring. In 1907 the Royal Navy had standardized its "Admiralty Pattern" rig based on the Siebe design.
With his trial-and-error testing completed and following interviews with working Navy and commercial divers, Stillson presented his document, The Report on Deep Diving Tests 1915, which contained a three-view drawing of a recommended helmet design that is immediately recognizable as the genesis of the MkV.
Stillson's recommended design varied from most of the contemporary commercial helmets in some important ways. Instead of three lights, it had four, adding one above the faceplate for an upward view. And the faceplate itself was unique in that it was hinged, whereas almost all faceplates of its day were of the screw-in variety (the hinged faceplate would make the MkV "sailor-proof," eliminating the possibility of a slip of the hand losing the faceplate overboard and rendering the entire rig useless).
One of the most popular aspects of Stillson’s design was the positioning of the exhaust control valve near the right front of the bonnet instead of behind the head, where it was often very difficult to reach and manipulate. The rear position was logical, because it kept the exhaust bubbles away from the faceplate and side lights, where they would obscure the diver's vision. Stillson resolved this by placing the actual valve near the diver's right jaw and ducting the bubbles back through an external "bananna tube" to an exhaust port in the conventional location at the rear.
The very first diving helmet ever built (by Augustus Siebe for the Deane brothers in 1829) had its inlet air ducted inside the helmet to flow out over the windows to keep the glass from fogging up. This became standard on virtually all the three-light helmets that followed. Adding Stillson’s top light, however, made ducting to the all-important faceplate somewhat difficult. So a “spit cock” valve was added adjacent to the faceplate on the right side so the diver could take in a mouthful of outside water to spit onto the faceplate to clear it (there wasn’t much concern over pollution or nuclear containment diving in 1915). The prototype U.S. Navy MkV diving helmet, produced by Morse in 1916, rather closely followed Stillson’s published design. Within a very short time, however, the “standard” MkV emerged with some slight variations: The spit cock was moved from the right side to the left, and the exhaust valve was moved further forward into its place. This permitted the spit cock to be on the opposite side of the helmet from the exhaust valve, so that in cases where the diver was working on his right side in mud or sand (which could plug up the exhaust port) the spit cock could be used as an auxiliary manual exhaust valve. Although some MkV’s were individually modified over the years, “official” variations were rare and subtle (the eight-point exhaust valve wheel was replaced by a four-point wheel, for instance, and the the vertical goosenecks at the back of the helmet were angled inward so that the communication and air supply lines would cross behind the diver’s back). Conventional helmet design in 1915 tended toward smaller bonnets to reduce the displacement of the helmet and its tendency to float, thus reducing the weight required to keep it down. The bonnet of the MkV is slightly bigger than most helmets of its time, and that trait proved to be one of its best features. The size gave it greater displacement and required more weight to neutralize, but the volume of available air made it an extremely comfortable helmet in which to work. The design had little to do with air volume, however, for the large bonnet was designed to go over a set of headphones and mouthpiece speaker worn by the diver for communications, even though the built-in two-way comm speaker was part of the original production model. The need for more weight to "sink" the helmet mandated the use of a weight belt rather than the breastplate weights then commonly in use. This actually made the rig much easier to handle both in the water and on the surface, as the weight was better distributed and focused around the diver's natural center of gravity, rather than being top-heavy around the chest.
The MkV differs from the Admiralty Pattern gear in that it is intended to be used with a weight belt rather than breastplate weights and also in being designed for use with an air control valve. The Admiralty Pattern rig was designed for use with a hand pump and depends on the surface operators to adjust the diver’s air flow through voice communication or liine-pull signals -- the diver himself has only the exhaust valve on the back of his helmet to control his buoyancy. The MkV was designed from the onset to be used with a power-driven air compressor and has an air control valve positioned for the diver’s left hand to regulate the incoming air (when being used with a hand pump, the MkV is generally dived with the air control valve wide open and the diver using the surface to regulate the air flow, to avoid the men on the pump having to work against a closed valve). With the air control valve, the MkV diver has total control of both inbound and exhaust air flow without having to communicate with the surface.
The Morse and Schrader companies produced the first MkV's (among the earliest in the Historical Diving Society members’ collections are Leon Lyons’ Schrader serial number H20 of 1917 and Leslie Leaney’s Morse 2289 of February 24, 1917). Judging by known serial numbers, Schrader produced about 600 World War I era MkV’s, and the Morse numbers are likely similar.
Public fame was achieved by the MkV in May 1939 when it was used by the Navy divers who reached the sunken U.S. submarine Squalus in 240 feet of water and subsequently rescued 33 crewmen from the bottom of the Atlantic. Air-supplied MkV’s were used for the initial Squalus rescue, and since the job took the divers about 50 feet deeper than is considered safe for air-supplied work (because of the dangers of nitrogen narcosis, which produces a dangerously "drunken" effect on the diver) the rescue divers were awarded the only Congressional Medals of Honor bestowed on anyone between the two World Wars.
Since heavy gear like the MkV is subject to exactly the same laws of physics that apply to today's scuba divers, a mixed-gas version of the MkV had been developed in the 1930s for work deeper than 180 feet. These replaced the nitrogen in the air mix with helium, which does not have the toxic effect under pressure of nitrogen, with a trickle of oxygen fed in to replace that breathed by the diver. A large canister of absorbent was attached to the back of the MkV gas hat to scrub the carbon dioxide from the diver's exhaled breath. Since helium conducts heat more rapidly than nitrogen, the MkV gas hat was designed for use with electrically-heater underwear -- an additinal gooseneck was built into the helmet for the power connection from the surface! All of this added weight to an already heavy rig, and the gas hats were equipped with lifting rings on the top to support the weight of the helmet with a hoist when the diver was dressing on the surface. Helium MkV’s were used for the long-term salvage operation on the Squalus. To keep the diver from venting the valuable helium gas accicentally, the spit cock was eliminated, and a fourth duct was added inside to ventilate the faceplate.
The MkV is as useful today as it was in 1917, and for some jobs there isn’t a modern rig that can match it. At a joint Historical Diving Society and Association of Diving Contractor’s affair in Santa Barbara, California, recently, somebody in the crowd watching a MkV diver being dressed commented, “Those old deep sea rigs are completely gone today.” An ADC dive contractor just looked over and matter-of-factly countered, “Oh yeah, well I’ve got six MkV’s in the water on jobs in the Midwest as we speak.”
