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Inside German WW2 submarines
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According to Karl Doenitz, if Germany had had 300 oceanic submarines instead of the 23 which were
ready at the outbreak of the Second World War, the events would have went differently from the beginning.
This article is dedicated to one of the best known types of submarines, which either because of the large number of units built,
its proven effectiveness or its undeniable aesthetics has left and indelible mark on the iconography of submarine warfare. It
is the U-Boat of the Type VII, and more particularly the C version and its variants 41, 42 and 43, for this was the most
popular of the series (from the A to the F) built during the war. The production of the Type VII was massive, with a total of
1452 units ordered, of which however the Kriegsmarine received only 709, due to diverse circumstances imposed by the state of
war. Out of these units, 665 were of the C version.
This production on a large scale was not achieved by a completely standardized construction as that of the Type XXI, a model
built by means of sections prefabricated in different factories to be later assembled in shipyards, following the idea originally
developed in United States for the merchant ships of the Liberty class. This was not the case of the Type VII, a model which
evolved gradually across its different models, which were at the same time modified during the assembly in seventeen different
shipyards, which applied peculiar technical solutions and particular finishes in the units delivered.
External disposition of the submarine
The concept of a double hull, in vogue in the late 19th century, evolved towards a single hull inspired in the UB III coastal
submarines launched in 1917, which had a displacement of 263 tonnes whilst surfaced. This meant that both the hydrodynamic and
pressure hulls were actually a same unit. The pressure hull was topped off in the aft and fore ends with a welded sheet metal
structure, which not being watertight eased the hydrodynamics of the ensemble both in the surface and in immersion. Upon
these two structures it was attached the deck, which was divided on its center by the conning tower, structure which housed the
pressurized attack room.
Life in the submarine took place inside the pressure hull of circular section, which had a diameter of 4.7 meters on its wider
part and a deck dividing it into two spaces of identical height. For its construction it was used Wotan weich
0.21% carbon galvanized steel sheet, with a thickness of 1.6 centimeters and reinforced to 2.2 centimeters on its most critical
point (the turret). The structure was divided into eight sections; only the two in the center were totally circular, whereas the
others had a truncated cone shape and were welded to each other. The ensemble was reinforced by an intrincate framework of
welded T-shaped ribs, placed at intervals of 60 centimeters. In the ends, two hemispheres with orifices for the torpedo tubes
topped off the ensemble.
The last element to be welded and riveted was an opening located behind the conning tower, throught which all the inner elements of
the submarine were introduced, from a simple nut to the huge Diesel engines, following a perfectly orchestrated process. The
first areas to be populated with mechanisms were the stern and the prow, and the last one was the central command area with its
periscopes. Once this process was finished, the opening was welded and so the hull became a watertight unit.
Two large water ballast tanks were welded to the sides of the pressure hull, which confered the submarine its characteristic shape.
The size of these tanks was successively increased through the different models, with the double purpose of housing more ballast
- to reduce the time required for the maneuver of immersion - and installing additional fuel tanks, which were filled with water
as the fuel was consumed, to control the trimming of the submarine.
As aforementioned, the outer hull was welded throughout the submarine as a second envelope, through which water flowed freely
across numerous openings to ease the maneuver of immersion. In the fore section they were located four torpedo tubes and their
mechanisms, the anchor, the winch, the chains' room, the trimming tanks to compensate the weight of torpedoes as they were launched,
ballast and a watertight room for spare parts. To the sides protruded the hydroplanes and their protection frames. Distributed
around the axle of the hydroplanes they were the orifices of the hydrophone (Gruppenhorchgerät) and just
above they were the diaphragms of the submarine telegraph (Unterwasser Telegraphie). The aft end of the
hull had a pointed shape to accelerate the stream of water, and housed the rear torpedo tube with its opening and trimming
mechanisms as well as the system of rudders and rear hydroplanes for navigation in surface and in immersion.
The structure of the deck was built of steel profiles with a teak planking attached to the upper surface, to avoid the formation
of ice crusts in the coldest latitudes. This surface resembled a true maze full of numerous hatches and box covers (used to access
the interior, introduce the torpedoes or store the ammunition of the 88-millimeter cannon), bitts and retractable winches and,
later, complements such as the snorkel and the four watertight containers on the prow for inflatable lifeboats (in the version
VIIC/44). In this structure they were stored as well, in the stern and the prow, two torpedoes in reserve in separate watertight
containers. Behind the conning tower it was located the inner ventilation system and the gas exhaust of the engines, with an
intrincate system of valves which caused many watertightness problems until its modification in 1940, and some casualties in
fast immersions beyond 50 meters.
Attached to the center of the hull the conning tower rose, molded of welded steel sheet and riveted on its different components.
This was perhaps the element of the external structure of the submarine which evolved the most along the war, with up to ten basic
types developed. In this article we will see the model adopted in 1944 (Turm 4). Its original purpose
was that of bridge for command and attack during navigation in surface, evolving during the course of the war until becoming a
parapet fitted with antiaircraft defense, incorporating to its design numerous offensive and defensive contraptions. In its
rear part, sharper than the fore one, they were located the orifices for the air intake of the crew, whereas the air intakes for the
Diesel engines were located in the solid parapet of the bridge.
The antiaircraft armament increased from 1942, when the SK C/35 88-millimeter deck cannon (equipped with 200 rounds) was definitely
removed. Other armaments were installed, from a simple C/30 20-millimeter cannon (equipped with 4380 rounds) in the "smoking deck"
to two C/38 MII 20-millimeter twin cannons and one Rheinmetall-Borsig LM 43 U 37-millimeter quick-firing cannon (equipped with 2000 rounds)
fitted with a protective shield, in the prolongation of the terrace known as "greenhouse" (Wintergarten).
In the center of the bridge planked with teak, a tube protected the surveillance periscope. Behind it there was a mounting with
a support for the UZO (Uberwasserzieloptik or Surface Targeting Binoculars). The binnacle, the supports
of the signals lamp and other elements such as the communications telescopic antenna were located in this area as well.
A longitudinal opening in the larboard parapet housed the directional antenna (Funkpielrahmen) which was used
to determine in surface the location coordinates of other ships from their radio transmissions. Later other electronic devices were
added, such as the Fu M029 GEMA radar, installed in the form of small antennas in the frontal area of the conning tower, and the
Fu M030, more visible due to its grill shape and retractable inside a rectangular receptacle in the starboard parapet. The Fu Mb Metox
radar detector and its famous cross-shaped wooden movable antenna (Biskayakreuz) did not have a fixed
position in the bridge, for it had to be disassembled and stored in the interior priorly to each immersion. In the late period
of the war, the adoption of the snorkel, contraption which allowed a partially submerged navigation through Diesel engines, added a
new element to the already saturated and somewhat chaotic conning tower.
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