The design effort began in mid-August 1914 and by mid-October the first 15 boats were ordered from two German shipyards.
Several of the first boats underwent trials in German home waters, but the rest were assembled and tested at either Antwerp or Pola.
In the earliest stages of the First World War the German Army's rapid advance along the North Sea coast found the German Imperial Navy without submarines suitable to operate in the narrow and shallow seas off Flanders.
[11][12] By 18 August 1914, two weeks after the German invasion of Belgium, the planning of a series of small coastal submarines had already begun.
[12] The German Imperial Navy stipulated that the submarines must be transportable by rail, which imposed a maximum diameter of 3.15 metres (10 ft 4 in).
The rushed planning effort[11]—which had been assigned the name "Project 34"—resulted in the Type UB I design, created specifically for operation from Flanders.
[1] The drivetrain of the boats consisted of a single propeller shaft driven by a Daimler (Germaniawerft) or Körting (Weser) diesel engine on the surface, or a Siemens-Schuckert electric motor for underwater travel.
[7] The German Imperial Navy ordered its first fifteen Type UB I boats on 15 October 1914.
Type UB I boats destined for service with the Flanders Flotilla (U-boote des Marinekorps U-Flottille Flandern) made a five-day journey to Antwerp for the two- to three-week assembly process.
[25] According to authors R. H. Gibson and Maurice Prendergast in their 1931 book The German Submarine War, 1914–1918, the UBs did not have enough power to chase down steamers while surfaced and lacked the endurance to spend any extended amount of time underwater, exhausting their batteries after little over an hour's running.
[25] In-service use revealed another problem: with a single propeller shaft/engine combination, if either component failed, the U-boat was almost totally disabled.
The boats were equipped with compensating tanks designed to flood and offset the loss of the C/06 torpedo's 1,700-pound (770 kg) weight, but this system did not always function properly;[27] as a result, when firing from periscope depth the boat could broach after firing or, if too much weight was taken on, plunge to the depths.
When UB-15 torpedoed and sank Medusa in June 1915,[28] the tank failed to properly compensate, forcing the entire crew to run to the stern to offset the trim imbalance.
[33] The Type UB I boats of the Flanders Flotilla originally patrolled the area between the United Kingdom and the Netherlands,[32] but began patrolling the English Channel after UB-6 pioneered a route past British antisubmarine nets and mines in the Straits of Dover in late June.
[37][38][c] The four remaining Type UB Is in Flanders—UB-10, UB-12, UB-16, UB-17—were all converted to minelayers by 1918, having their torpedo tubes removed and replaced with chutes to carry up to eight mines.
[37] UB-9 was initially assigned to the Baltic Flotilla,(U-boote der Ostseetreitkräfte V. U-Halbflottille) and was joined by UB-2 and UB-5 in early 1916.
[31] The three Type UB I boats of the Constantinople Flotilla seem to have patrolled primarily in the Black Sea.
UB-8 was transferred to the Bulgarian Navy in May 1916,[41] and UB-7 disappeared in the Black Sea in October 1916,[42] leaving UB-14 as the sole remaining German Type UB I in the flotilla;[43] she was surrendered at Sevastopol in November 1918 to French armies stationed there during the Russian Civil War.
[3] Known as the U-10 or the Okarina (Ocarina) class as a part of the Austro-Hungarian Navy,[46] the five boats operated primarily in the Adriatic in patrols off Italy and Albania.
U-16 was sunk after she torpedoed an Italian destroyer in October 1916, and the remaining three (and the unrepaired U-10) were ceded to Italy at the end of the war.