MINE AND BOOBY-TRAP DISPOSAL
The experimental Unit was next called in to assist in the
counter-measures against the growing menace of German mine warfare.
After the finding of the first magnetic mines, it became imperative that
mines laid near the coasts should be examined before they were destroyed
by sweeping, so that new methods of firing them could be detected at
once. A number of officers and ratings were recruited for the hazardous
task of examining and, if necessary, recovering these mines by diving on
them. The use of ordinary diving equipment was prohibited, as it
involved risk to too many lives in the diving boats, and various
components were considered dangerous in the presence of magnetic and
acoustic mines. It is desirable, too, for obvious reasons, that there
should be no delay in regaining the surface, such as would be involved
in the carrying out of routine decompression. Self-containing oxygen
apparatus suggested itself, but the depth required was too great, as it
may well be imaginated that a visit from “Oxygen Pete” would have been
most unwelcome when dealing with a mine.
The Experimental Unit further developed the oxy-nitrogen mixture system
already used in Siebe’s self contained diving dress before the war.
Formulae were calculated so that the suitable proportions of nitrogen
and oxygen could be worked out for various depth and conditions in order
that the risk of ‘bends’on the one hand, and of oxygen poisoning on the
other, could be kept to a minimum.
The experiments resulted in the adoption of the Siebe Gorman Mine
Recovery Suit (M.R.S.), a two-piece self-contained helmet suit (R.H. and
R.W.G. Davis patent), using a mixture of oxygen and nitrogen which
enabled the diver to surface freely from 72 feet without stops, and from
120 feet with only a few minutes on the shot rope. It was, in fact,
possible to ascend immediately from 120 feet in emergency with only a
slight risk of bends.
Every piece of metal in this suit had to be non-magnetic; aluminium
alloy cylinders were used and even such minor items as reducing valve
springs and buckles on straps had to be specially made of non-ferrous
metal. Non-magnetic steel knives were specially developed and tested.