It's hard to overstate the profound impact that NEDU has had on recreational Scuba diving. NEDU stands for the US Navy Experimental Diving Unit and is often referred to as EDU or just "The Unit". Everything from diving physiology, equipment, testing, and safety is influenced by their work.
In the Beginning
NEDU's roots were pretty humble. Chief Warrant Officer George D. Stillson is credited with the Navy's first experimental diving work at the Brooklyn Navy Yard in 1912. That effort produced:
Mysterious symptoms of what we now realize is Decompression sickness or the "bends" were observed soon after Augustus Siebe began manufacturing his surface-supplied diving dress in the 1830s. Greek sponge divers, caisson workers or "Sand Hogs", and salvage divers all noted debilitating effects of deep and long duration dives. Unfortunately decompression tables to avoid DCS were not developed until Haldane and Stillson so these divers had little to depend on besides sea stories handed down by old and often injured divers.
Haldane's work was built on Sir Robert Boyle's experiments that observed bubbles in eyes during animal experiments in 1670 and Paul Bert's work that described the cause of DCS and the benefits of breathing pure Oxygen in 1878. Stillson, who was not a physiologist or physician, improved and extended Haldane's tables through animal and human testing.
Chief Stillson's assignment coincided with the development of early submarines, and the tragic accidents that accompanied them. Stillson and his divers were sent to salvage the submarine F-4 after she sank off Pearl Harbor Hawaii with all hands in 1915. She was in 306'/93M of water. Divers experienced severe impairment caused by Nitrogen Narcosis which prompted the US Bureau of Mines to suggest Helium-Oxygen as a breathing mixture.
Testing of HeO2 mixtures and decompression table development began at the Bureau of Mines Experiment Station in Pittsburgh, Pennsylvania in conjunction with U.S. Navy Bureau of Construction and Repair. There are reports in 1924 that suggest than manned chamber dives were conducted after animal testing. The first operational use of HeO2 was on the private salvage the Steamship Lakeland that sank in more than 200' of water in Lake Michigan.
The submarine S-51 was lost in 1925 at a depth of 130'/40M of water off Block Island (Rhode Island, USA). Three of the 36 man crew survived. Salvage was led by Lieutenant Commander (later Rear Admiral) Edward Ellsberg and was chronicled in his book, On the Bottom (highly recommended). The S-4 sank in 1927 with all hands and was salvaged by Ellsberg's divers in 1928.
Establishing the Experimental Diving Unit
Submarine and crew losses dictated the need for trained divers and submarine rescue systems. NEDU was established in 1927 at the Navy Gun Factory in Washington DC and the Naval School of Diving and Salvage was authorized soon after. The gun factory later became the Washington Navy Yard.
EDU and the school were housed in a two-story brick building with near mirror-image floor plans. Each had two matching chamber complexes rated for 785'/239M of sea water. Each of the four complexes consisted of a horizontal double-lock decompression chamber connected to a vertical double-lock "wet pot" on the second deck. The wet pot was about 9'/2.7M in diameter and extended through the deck and rested on the first deck. The upper section was dry with a center access to water-filled space below. It was the largest hyperbaric facility at the time. EDU's chambers were constantly modified over the years to increase their pressure/depth ratings and support increasingly sophisticated environmental controls, instrumentation, and equipment testing.
Lieutenant (later Vice Admiral) Charles "Swede" Momsen was among the first officers assigned to EDU. He qualified on Submarines in 1922 and later commanded the refurbished S-1, which was assigned to sub-rescue testing duty. He led the development of the Momsen lung for submarine escape and the McCann Submarine Rescue Chamber. The McCann bell was still standard equipment on ASRs (submarine rescue ships) when I was in school and was included in our training.
EDU had a lot of basic questions to answer. Nobody knew how long a submariner could be exposed to pressure and how fast he could shoot to the surface without getting bent or suffer an embolism. Exhaustive human testing was conducted which ultimately lead to No Decompression Tables used by Scuba divers for decades.
The first Navy Medical Doctors didn't begin working with NEDU until mid-1930. They included Charles Shilling and Albert Behnke. Dr. Behnke did pioneering research on nitrogen (and inert gas) narcosis, recompression treatment and the use of Oxygen, Helium-Oxygen gas mixtures, and decompression theory to name a few. On a personal note, I had the opportunity to hear Dr. Behnke speak in 1967 at the UCSF's Applied Diving Physiology extension course. It seems like his name appeared in the footnotes on everything I read on diving physiology after that. The first Behnke Award was issued in 1969 by the Undersea and Hyperbaric Medical Society.
Edit: Corrected and updated Helium-Oxygen history with the assistance of @Oceanaut
It helps to understand
how little was known about
diving in the early 1900s
how little was known about
diving in the early 1900s
In the Beginning
NEDU's roots were pretty humble. Chief Warrant Officer George D. Stillson is credited with the Navy's first experimental diving work at the Brooklyn Navy Yard in 1912. That effort produced:
- The Navy's first diving manual published in 1916
- The USN's first Decompression tables (based on John Scott Haldane's work that was commissioned by the British Admiralty in 1907-8). Fleet diving operations were extended from 60'/18M to 250'/76M on air.
- The design and specifications for the US Navy's first standardized diving dress (precursor to the Mark V hat) and support systems.
Mysterious symptoms of what we now realize is Decompression sickness or the "bends" were observed soon after Augustus Siebe began manufacturing his surface-supplied diving dress in the 1830s. Greek sponge divers, caisson workers or "Sand Hogs", and salvage divers all noted debilitating effects of deep and long duration dives. Unfortunately decompression tables to avoid DCS were not developed until Haldane and Stillson so these divers had little to depend on besides sea stories handed down by old and often injured divers.
Haldane's work was built on Sir Robert Boyle's experiments that observed bubbles in eyes during animal experiments in 1670 and Paul Bert's work that described the cause of DCS and the benefits of breathing pure Oxygen in 1878. Stillson, who was not a physiologist or physician, improved and extended Haldane's tables through animal and human testing.
Chief Stillson's assignment coincided with the development of early submarines, and the tragic accidents that accompanied them. Stillson and his divers were sent to salvage the submarine F-4 after she sank off Pearl Harbor Hawaii with all hands in 1915. She was in 306'/93M of water. Divers experienced severe impairment caused by Nitrogen Narcosis which prompted the US Bureau of Mines to suggest Helium-Oxygen as a breathing mixture.
Testing of HeO2 mixtures and decompression table development began at the Bureau of Mines Experiment Station in Pittsburgh, Pennsylvania in conjunction with U.S. Navy Bureau of Construction and Repair. There are reports in 1924 that suggest than manned chamber dives were conducted after animal testing. The first operational use of HeO2 was on the private salvage the Steamship Lakeland that sank in more than 200' of water in Lake Michigan.
The submarine S-51 was lost in 1925 at a depth of 130'/40M of water off Block Island (Rhode Island, USA). Three of the 36 man crew survived. Salvage was led by Lieutenant Commander (later Rear Admiral) Edward Ellsberg and was chronicled in his book, On the Bottom (highly recommended). The S-4 sank in 1927 with all hands and was salvaged by Ellsberg's divers in 1928.
Establishing the Experimental Diving Unit
Submarine and crew losses dictated the need for trained divers and submarine rescue systems. NEDU was established in 1927 at the Navy Gun Factory in Washington DC and the Naval School of Diving and Salvage was authorized soon after. The gun factory later became the Washington Navy Yard.
EDU and the school were housed in a two-story brick building with near mirror-image floor plans. Each had two matching chamber complexes rated for 785'/239M of sea water. Each of the four complexes consisted of a horizontal double-lock decompression chamber connected to a vertical double-lock "wet pot" on the second deck. The wet pot was about 9'/2.7M in diameter and extended through the deck and rested on the first deck. The upper section was dry with a center access to water-filled space below. It was the largest hyperbaric facility at the time. EDU's chambers were constantly modified over the years to increase their pressure/depth ratings and support increasingly sophisticated environmental controls, instrumentation, and equipment testing.
Personal Sidebar
EDU was legendary to me in 1970 when I started First Class Diving School. I learned about it from my SCUBA instructor in 1962 who encouraged me to buy a Navy Diving Manual. Countless articles in Skin Diver Magazine elevated it to mythical proportions in my teenage mind. I was 20 by then but was still awed by the place.
These chambers didn’t look much different at the diving school when I was there, but you could barely see them on the EDU side of the building because of all the instrumentation, environmental control systems, calibration gas bottles, control consoles, and support for saturation diving experiments. I was able to get a few invitations when classified gear was out of view. Buying a few drinks in the Green Derby across the Anacostia River also helped.
The Navy Yard was an odd mix of junk and history. The Bathyscaph Trieste that made the record setting 35,797'/10,911M dive in the Mariana Trench in 1960 was mothballed across the street. It is now displayed at the National Museum of the United States Navy . A few vintage naval guns were strewn around and Franklin Roosevelt's presidential yacht, the USS Sequoia, was moored in the Anacostia next the school's diving stations. We were told that a fully-restored white PT boat moored next to her was used as a presidential escape boat. As the story goes, it would take the president out to open sea to transfer to a nuclear sub that was always on station during a crisis. EDU's goat pens for animal studies seemed to fit right in.
EDU was legendary to me in 1970 when I started First Class Diving School. I learned about it from my SCUBA instructor in 1962 who encouraged me to buy a Navy Diving Manual. Countless articles in Skin Diver Magazine elevated it to mythical proportions in my teenage mind. I was 20 by then but was still awed by the place.
These chambers didn’t look much different at the diving school when I was there, but you could barely see them on the EDU side of the building because of all the instrumentation, environmental control systems, calibration gas bottles, control consoles, and support for saturation diving experiments. I was able to get a few invitations when classified gear was out of view. Buying a few drinks in the Green Derby across the Anacostia River also helped.
The Navy Yard was an odd mix of junk and history. The Bathyscaph Trieste that made the record setting 35,797'/10,911M dive in the Mariana Trench in 1960 was mothballed across the street. It is now displayed at the National Museum of the United States Navy . A few vintage naval guns were strewn around and Franklin Roosevelt's presidential yacht, the USS Sequoia, was moored in the Anacostia next the school's diving stations. We were told that a fully-restored white PT boat moored next to her was used as a presidential escape boat. As the story goes, it would take the president out to open sea to transfer to a nuclear sub that was always on station during a crisis. EDU's goat pens for animal studies seemed to fit right in.
Lieutenant (later Vice Admiral) Charles "Swede" Momsen was among the first officers assigned to EDU. He qualified on Submarines in 1922 and later commanded the refurbished S-1, which was assigned to sub-rescue testing duty. He led the development of the Momsen lung for submarine escape and the McCann Submarine Rescue Chamber. The McCann bell was still standard equipment on ASRs (submarine rescue ships) when I was in school and was included in our training.
EDU had a lot of basic questions to answer. Nobody knew how long a submariner could be exposed to pressure and how fast he could shoot to the surface without getting bent or suffer an embolism. Exhaustive human testing was conducted which ultimately lead to No Decompression Tables used by Scuba divers for decades.
The first Navy Medical Doctors didn't begin working with NEDU until mid-1930. They included Charles Shilling and Albert Behnke. Dr. Behnke did pioneering research on nitrogen (and inert gas) narcosis, recompression treatment and the use of Oxygen, Helium-Oxygen gas mixtures, and decompression theory to name a few. On a personal note, I had the opportunity to hear Dr. Behnke speak in 1967 at the UCSF's Applied Diving Physiology extension course. It seems like his name appeared in the footnotes on everything I read on diving physiology after that. The first Behnke Award was issued in 1969 by the Undersea and Hyperbaric Medical Society.
Edit: Corrected and updated Helium-Oxygen history with the assistance of @Oceanaut
Continued in the next post
