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 crew-members 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.
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.
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 crewmembers 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.
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 Submergence 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.
Prior to the introduction of rescue systems, crewmembers trapped in a submarine were left to their own devices.
In 1911, two Royal Naval officers, (in collaboration 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.
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.
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.
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.