The Type UB I were in active service from March 1915 through the end of the war, with half of the 20 boats lost during the war.
UB-10 was eventually joined in the Flanders Flotilla by
UB-2,
UB-4,
UB-5,
UB-6,
UB-12,
UB-13,
UB-16, and
UB-17; of these, only
UB-2 made the journey to Flanders by sea rather than rail. and was responsible for sinking the first ship sent down by the flotilla. The Type UB I boats of the Flanders Flotilla originally patrolled the area between the United Kingdom and the Netherlands, Over the Type UB Is' first year of service,
UB-4 and
UB-13 were both lost, and
UB-2 and
UB-5 were transferred to the Baltic Flotilla. In March 1917,
UB-6 ran aground in Dutch waters and was interned for the rest of the war, along with her crew. 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 hull extended to . Their torpedo tubes were removed, and replaced with four mine tubes to carry eight mines. All but
UB-10 were lost in 1918;
UB-10, in poor repair and out of service, was
scuttled in October 1918 when the Germans evacuated from Flanders.
Baltic Flotilla UB-9 was initially assigned to the Baltic Flotilla,() and was joined by
UB-2 and
UB-5 in early 1916. All three became training boats at Kiel in 1916, Little information is available about the Type UB I boats operating in the
Baltic.
Constantinople Flotilla Four of the German Imperial Navy boats—
UB-3,
UB-7,
UB-8, and
UB-14—were selected for service with the Constantinople Flotilla. () All were sent to Pola for assembly and trials there as part of the
Pola Flotilla() before sailing on to join the Constantinople Flotilla.
UB-3 disappeared en route to Constantinople in May 1915, leaving
UB-14 as the sole remaining German Type UB I in the flotilla; she was surrendered at
Sevastopol in November 1918 to French armies stationed there during the
Russian Civil War.
Austro-Hungarian Navy UB-1 and the still incomplete
UB-15 were sold to the Austria-Hungary in February 1915; both were dismantled and shipped to Pola in May. After one cruise under the German flag, each boat was
commissioned into the Austro-Hungarian Navy. The pair—renamed
U-10 and
U-11, respectively—were joined by
U-15,
U-16, and
U-17 in October. the five boats operated primarily in the
Adriatic in patrols off Italy and
Albania.
U-10 (ex
UB-1) hit a mine in July 1918 and was beached, but had not been repaired by the end of the war.
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. In addition, four Type UB Is (assigned to the Pola Flotilla based at the Austro-Hungarian Navy's main naval base at Pola were assigned Austro-Hungarian designations. These were (as
U-9), (as
U-7), (as
U-8), (as
U-26). These four boats remained under commission in the German Imperial Navy, retained German crews and commanders, and received orders from the German flotilla commander at Pola.
Bulgarian Navy Germany and Bulgaria negotiated the purchase of two UB I boats for the Bulgarian Navy, and , in 1916. Two crews of Bulgarian sailors were sent to Kiel for training. Before the purchase could be completed,
UB-7 was sunk, leaving only one boat for Bulgaria. On 25 May 1916,
UB-8 was officially transferred to Bulgaria for the remainder of the war and renamed
Podvodnik No. 18 (in Cyrillic: Подводник No. 18). She was Bulgaria's first submarine, and was engaged primarily in coastal defense duties off Bulgaria's main Black Sea port of
Varna.
Podvodnik No. 18 survived the war and was ceded to France after the
Treaty of Neuilly-sur-Seine. == Footnotes ==