German version of the Snorkel
USS Torsk - last ship to sink enemy vessel in
World War II: One of several Tench Class submarines still located inside the
United States. Nicknamed the "Galloping Ghost of the Japanese Coast,"
the vessel is the only ship of the United States Navy to be named for the torsk
fish. Torsk received two battle stars for World War II service and the Navy
Commendation Medal for her service during the Cuban Missile Crisis. She set the
all-time record of career dives, at 11,884. She is also the only submarine
converted in the Fleet Snorkel program that has the original snorkel.
The Russian BARS CLASS
of 1915, the Kuguar, was fitted with a telescoping tube
to supply air to operate the diesels while submerged, a forerunner of the
snorkel.
To reduce the unbearable losses inflicted by radar equipped
escorts and aircraft, U-boat designers resuscitated an idea they had found in
captured Dutch submarines in 1940. The Schnorchel (nostril) was an air mast,
originally intended to ventilate the interior of the boat, but in 1943 it
promised a way to allow a U-boat to recharge its batteries without surfacing.
The diesel-generators could be run at full power, while a masthead float valve
prevented water from flooding the boat (small amounts of water were vented
outboard). Used in rough weather it caused extreme discomfort to the crew by
causing rapid changes in air pressure, but the alternative was destruction.
In practice the Schnorchel (later Americanised to 'snorkel')
did some damage to morale, and some of the inexperienced U-boat commanders were
reluctant to use it for long periods. Radar warning receivers were used to
detect hostile transmissions, but the performance of Allied radars outpaced the
German scientists' efforts to counter them. Rubber coatings were used to absorb
sonar energy and the pillenwerfer bubble decoy was introduced. It functioned
like a giant Alka Seltzer, producing flat bubbles in the water, but experienced
asdic operators rarely mistook them for genuine targets.
THE GUPPY PROGRAMME
In 1946, the US Navy began its Greater Underwater Propulsive
Power (GUPPY) programme, upgrading the large number of 'Gato', 'Balao' and
'Tench' class boats built during the war.
The basic elements of the GUPPY conversion included
streamlining the hull and augmenting underwater power. The prototypes Odox and
Pomodon were originally intended to act as fast targets for training surface
anti-submarine forces, and to cope with an expected improvement of performance
in Soviet submarines. The conning tower was replaced by a streamlined 'sail',
which enclosed periscopes and snorkel mast. The characteristic buoyant bow
(intended to improve surface performance) was replaced by a round bow, and
every possible piece of equipment likely to cause resistance was either removed
or made retractable. It was not easy to find space internally for more battery
cells because the wartime fleet boats were by no means spacious. The solution
was to remove the auxiliary diesel-generator from the after-engine room and
reposition it in the space formerly occupied by the magazine for the redundant
deck-gun.
Much work had to be done on battery technology to achieve
higher output. By accepting a shorter life (18 months) and designing a smaller
battery-cell, it was possible to provide four main batteries of 126 cells each
(the original boats had only two). This brought new problems, for the
high-capacity batteries generated more hydrogen and heat, increasing the risk
of fire and explosion. After experimenting with a closed-cell system the US
Navy reverted to a water-cooled opencell system, and the air-conditioning
equipment was boosted by nearly 300 percent to handle the extra load. Apart
from minor teething troubles the GUPPY I conversion proved successful. A
simultaneous programme to improve the snorkel was running at Portsmouth Navy
Yard in New Hampshire. The basic problem was that exhausting gases underwater
created more back-pressure than the diesels could handle. The American
two-cycle diesels suffered pressure fluctuations when the float valve closed,
whereas the wartime German four-cycle diesels were not badly affected. Some
components of the Fairbanks Morse and General Motors diesels were redesigned to
cope with the stresses, but the ultimate solution was to replace the simple
float valve with an air-actuated head valve designed to act rapidly and
positively. The opening and closing was now controlled by three electrodes
located near the snorkel head. When a wave broke over the head it completed a
circuit, directing air to shut the valve.
The exhaust mast was designed to be raised with the
induction mast, and to ride about 1.21-2.4m (4-8ft) below the surface. The
exhaust port was fitted with baffles to reduce the amount of smoke and haze
reaching the surface. A mast similar to that in the Type XXI boats was tried in
the USS hex in 1947, but it threw up a highly visible plume of spray. The US
Navy boats, being much larger than the U-boats, needed a much bigger snorkel
head and mast to draw in sufficient air, and a major redesign of the head was
needed to reduce the plume. Three types of snorkel were developed: the original
GUPPYI type; a simpler type for the unmodernised fleet boats, and a
sophisticated type for fast attack boats. Even nuclear submarines need
snorkels; they are needed if the boat is running on the auxiliary
diesel-electric system, and it is still the quickest way to rid the interior of
the boat of the various contaminants which cannot be absorbed by the
air-purification system.