The U class was a series of small attack submarines built for the Royal Navy, launched between 1937 and 1943. These were initially
intended as unarmed training vessels to be used as practice targets in antisubmarine training exercises. The first three units
built were modified to accommodate six torpedo tubes on the bow, four internal to the pressure hull and two external. From the third
unit onwards, every vessel was equipped as well with a 76-millimeter deck cannon, but the first boats that received this weapon lacked
a purpose-made hatch for the gunners, who had to use the hatch on the sail. It had to be a race against time to return the ammunitions
inside the submarine during a crash dive.
These submarines featured a single hull of riveted construction, divided into three watertight compartments, with both the ballast and fuel
placed internally. Due to the small size of these boats, the living conditions onboard were far from comfortable. Being in origin modest
training units, these submarines suffered from tactical shortcomings, due to reduced periscope depth and lack of a calculator capable of
programming the gyroscopes of individual torpedoes, a feature necessary for attacking different targets in a torpedo salvo. Nonetheless,
the submarines of the U class proved to be useful in the confined waters of the North Sea and specially in the Mediterranean.
The small size of the hull prevented these submarines from being powerful units, but it allowed an excellent maneuverability
and a fast production. During the war the largest part of the units served with the 10th Submarine Flotilla based in Malta. One of those
was the HMS Upholder depicted in the illustration; she is painted with the Mediterranean Blue camouflage adopted for diminishing the risk
of being detected by enemy aircraft while in immersion. Note also the lack of a deck gun and the bulbous bow housing two external
torpedo tubes. This prominence was criticized because it impaired vision at periscope depth and therefore was adopted only in the first seven units
built.
During the war nineteen units were lost, thirteen in the Mediterranean and the rest in the North Sea and Atlantic Ocean. The HMS Untamed,
sunk in May 1943, was salvaged and rebuilt to be later recommissioned as HMS Vitality. From 1941, some of the boats were transferred to
the Soviet Union, the Free France and other Allied navies. After the war, the largest part of the units was withdrawn from active service and
subsequently sold for scrap, but some of them returned to their training role during some time.
U class: 49 units - 3 units Group 1 (Undine, Unity, Ursula); 12 units Group 2 (Umpire, Una, Unbeaten,
Undaunted, Union, Unique, Upholder, Upright, Urchin, Urge, Usk, Utmost); 34 units Group 3 (Uproar, P32, P33, Ultimatum, Umbra,
P36, Unbending, P38, P39, P41, Unbroken, Unison, United, Unrivalled, Unruffled, P47, P48, Unruly, Unseen, P52, Ultor, Unshaken,
Unsparing, Usurper, Universal, Untamed, Untiring, Varangian, Uther, Unswerving, Vandal, Upstart, Varne, Vox)
Type: Attack submarine
Length: 58 meters
Beam: 4.9 meters
Draught: 4.6 meters
Displacement (surfaced): 540 tonnes standard, 630 tonnes full load
Displacement (submerged): 730 tonnes
Propulsion: 2 x shaft, 2 x Diesel-electric group Paxman Ricardo, 2 x electric motor (615 horsepower with generator, 825 horsepower with batteries)
Speed (surfaced): 10.5 knots (19.5 kilometers/hour)
Speed (submerged): 8.5 knots (15.7 kilometers/hour)
Range (surfaced): 3800 nautical miles (7037 kilometers) at 10 knots
Range (submerged): 150 nautical miles (277 kilometers) at 2.5 knots
Test depth: 60 meters
Complement: 27-31
Armament: 4-6 x 533-millimeter torpedo tube (4 internal at prow, 2 external at prow in some units), 8-10 x torpedo,
1 x 76-millimeter 45-caliber deck cannon, 3 x 7.7-millimeter Lewis machine gun
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