Diving  is a  potentially  hazardous  activity.  The materials  contained within  this  magazine  are for informational purposes only and are not intended as a substitute for proper and appropriate training.

Submarine Escape

by David Strike

Surface Rescue The first practical  demonstration of a surface rescue attempt occurred in May, 1939, with the  use of  the McCann  Rescue  Chamber - a  large diving bell  with an  upper  and lower chamber  and crew  of two - that  successfully  brought  to  the  surface  surviving crew- members of the USS Squalus from a depth of about 70-metres. Divers first  assessed the  damage  and determined  that  the submarine  was  lying on  an almost even keel with the escape hatches  uppermost and cleared of any debris that might hinder the rescue.  They then attached  a heavy-duty cable from the surface that allowed the chamber  to winch itself  down to the  submarine.  Once  positioned  over  the escape hatch with a watertight seal established, seven  or eight crewmembers at a time could exit the submarine, close both hatches behind them, and be brought to the surface.

To go down? In early  submarine designs breathing conditions  deteriorated quickly.  Where the sunken craft  lay in  water  depths  accessible  to  a  diver there  was always  the  possibility  of attaching  a surface supplied air hose into the hull before attempting to raise  the vessel, a  lengthy  and  weather-dependent  process that  rarely  met  with success in  terms of managing to save the crews. …or to come up? A better option  in these circumstances  was to provide  the  survivors  with  a means of exiting their sunken submarine without compromising any of the remaining air spaces, and to develop a compact self-contained  breathing apparatus enabling them to  safely reach the surface.

Building on the  lessons learned from  the past, submarine disasters are now a rarity, but when they do occur the problem arises of what can be done to assist the crew. Because of  possible damage  to life  support  systems,  time  is  the  critical  factor.  For surviving crewmembers  trapped inside a crippled submarine there are two alternatives; a surface mounted  rescue attempt; or an effective  means of managing  their own escape. Both methods  face similar problems  and drawbacks,  not  least the  depth  and angle at which  the vessel rests; how  quickly surface  support can be mobilised  and arrive at the scene; and the surface weather conditions.

Diagram of the McCann Rescue Bell

Read more about the Squalus incident here

The  diver's role  was critical  to  this  type  of rescue:  A  consideration  that  prompted  the introduction   of   mixed  gas  diving   and  the military deep diving  experiments  of the 'fifties and 'sixties. Although the device was introduced into many of the  world's  Navies  there  was  a  growing appreciation  of its  limitations as far as depth was concerned, a drawback  that  led  to  the design  and introduction  by the US  Navy of a new  type  of  rescue  craft;  the  Deep  Sub- mergence Rescue Vehicle (DSRV). Equipped  with sonar and  able to  safely go to depths   comparable    with   those   of   most submarines,  DSRV's  are  self-sufficient   craft intended for quick deployment.

In June,  1931, the DSEA proved its  worth when a group  of survivors from the submarine, HMS Poseidon, made  an escape to the  surface of the South China Sea.  The submariners equivalent of a parachute, the DSEA paved the way for the introduction of similar devices, such as the US Navy's 'Momsen Lung', into other submarine fleets. Improvements   on  these  basic  systems  have  since  led  to  the  introduction  of  more sophisticated Hood  Inflation  Systems  combined  with  immersion  suits for buoyancy  and thermal protection when on the surface. Now  provided  with a means  of  breathing,  survivors  also  have  to  be  able to  exit the submarine.  The  two  methods  consist  of  Compartment  escape  and  Chamber  escape.

Submarine Escape Prior to the introduction of rescue systems, crewmembers trapped in a submarine were left to their own devices.  Escape Apparatus

In 1911,  two  Royal Naval  officers, (in collab- oration  with  Robert Davis, of Siebe, Gorman & Co,),  designed   the  world's   first  submarine escape  apparatus.  Consisting of a jacket and helmet,  the   wearer   was   provided  with  a  mouthpiece and   breathing  hoses attached to a canister of "oxylithe", a  chemical  compound that absorbed expired carbon dioxide. Proving  too bulky  for practical  use,  the Hall- Rees helmet  was  eventually  superseded by a streamlined,   lightweight    unit,    the    Davis Submerged     Escape     Apparatus     (DSEA). Consisting  of  a  breathing  bag, (or  counter- lung), a  canister  of  CO2  absorbent,  oxygen cylinder,  breathing  hose,  mouthpiece,  nose- clip and  goggles, the DSEA was  installed in all RN submarines.

Chamber escape Built beneath a hatch opening, an escape chamber allows one, or more, personnel to enter by an  access  door from  the  submarine's  compartment.  Once  this  door  is  closed and sealed, the chamber's occupant can control the  compartment's flooding by sea-cocks and vent the  compressed air  bubble that  builds  up under the overhead  escape hatch cover. As soon as this  is completed,  the outer  hatch is opened  and the crewman  can escape. The remaining survivors  close the outer hatch  mechanically; drain the water to the bilges and make the chamber ready for the next escape cycle.

At the surface Following an escape the survivors' problems are far from over.  Arriving at the surface they must hope  for benign weather and  sea conditions - and that they're  quickly picked up by rescue craft with the necessary onboard medical and hyperbaric facilities. For submariners the choice between  waiting to be rescued or attempting an escape is not an easy one to make.

Compartment escape This system involves  flooding the whole compartment  until the air  is compressed and the water ceases  to rise.  A trunk  is  then attached or  lowered from the  base of the escape hatch  until it rests  beneath the  surface  of  the  water.  Valves  allow  the  trunk  to be completely  flooded,  at  which  point  the  hatch  can  be  opened  without  releasing  the compartment's air pocket.  Donning their  escape apparatus the crewmembers  duck down, one at a time, enter the tube and ascend to the surface. Because of the  need to maintain  a sufficiently  large  air pocket  that  allows survivors to breathe while awaiting  their turn to escape,  the compartment method is  only effective in comparatively  shallow water  depths.  Dedicated  escape  chambers, on  the  other hand, allow escapes from depths in excess of 180 metres.