She had been laid down in February 1914 as U-11 the final boat of the U-7 class for the Austro-Hungarian Navy (German: Kaiserliche und Königliche Kriegsmarine or K.u.K.

After the outbreak of World War I in August 1914, the Austro-Hungarian Navy became convinced that none of the submarines of the class could be delivered to the Adriatic via Gibraltar.

A part of the IV Flotilla throughout the war, U-70 sank 52 merchant ships with a combined gross register tonnage (GRT) of 135,288.

The Austrian specifications called for two shafts with twin diesel engines (2,300 metric horsepower (2,269 bhp; 1,692 kW) total) for surface running at up to 17 knots (31 km/h; 20 mph), and twin electric motors (1,240 metric horsepower (1,223 shp; 912 kW) total) for a maximum of 11 knots (20 km/h; 13 mph) when submerged.

[9][Note 6] Germany began its second submarine offensive against shipping in February 1916, the month U-70 had joined the IV Flotilla.

As in the first submarine offensive, U-boats were sent independently around Scotland to patrol the Irish Sea and the western entrance to the English Channel.

[11] U-70 sank her first ship on 16 March,[12] when she dispatched the British sailing vessel Willie 60 nautical miles (110 km; 69 mi) northwest by west of Fastnet Rock.

[13] The same day she also damaged the British cargo ship Berwindale, en route to Avonmouth with a load of wheat from Galveston, Texas.

The other two other boats, U-43 and U-44, were stationed off Pentland Firth, in position to attack the British fleet leaving Scapa Flow.

All the boats were to remain on station until 1 June and await a coded message which would report the sailing of the British fleet.

[12] From the early stages of the war the British had blockaded Germany, preventing neutral shipping from reaching German ports.

By the time of the so-called "turnip winter" of 1916–17, the blockade had severely limited imports of food and fuel into Germany.

[22] With the blockade having such dire consequences, Kaiser Wilhelm II personally approved a resumption of unrestricted submarine warfare to begin on 1 February 1917 to help force the British to make peace.

[24] The first recorded action of U-70 under the new rules of engagement occurred near the end of February 1917, when the U-boat shelled the British-flagged SS San Patricio.

[27] Southland was carrying a general cargo from Liverpool to Philadelphia when U-70 sank her at position 56°10′N 12°14′W / 56.167°N 12.233°W / 56.167; -12.233, some 140 nautical miles (260 km; 160 mi) from Tory Island.

[12] Rhododendron had been constructed in 1917 as a purpose-built Q-ship, a warship disguised as a merchant ship to lure German submarines within range of their concealed gun batteries.