U-8 was one of four type U-5 class submarines. Ordered on 8th April 1908, her keel was laid down on 19th May 1908 in the Garmaniawerft shipyard in Kiel. Launched on 14 March 1911, and commissioned on 18th June 1911. In command of U-8 from 1st August 1914 to 31st August 1915 was Konrad Gansser, and from 1st September 1914 to 4th March 1915 Alfred Stoß, who sank while on patrol five ships, the Branksome Chine, and Oakby on 23rd February 1915, and on 24th February 1915, Harpalion, Rio Parana, and Western Coast a total of 15.049 tons.

Type U-5 class submarines were a single-hulled design boat of 105 feet long and displaced 240 tonnes on the surface and 273 tonnes submerged. The two bow torpedo tubes had unique, cloverleaf-shaped design hatches that rotated on a central axis, and carried four torpedoes. The boats were powered by twin 6-cylinder gasoline engines while surfaced, and twin electric motors submerged, which drove the 2 screw propellers of speeds of 13.5/10 knots. U-8 carried a crew of 28.

On 4th March 1915 the German Submarine U-8, while on patrol in the channel became a victim of the Channel's anti-submarine defences becoming trapped in nets, and in so doing setting off the net alarms she was forced to surface. The submarine was spotted in heavy fog by HMS Viking and she opened fire, making the submarine submerge. The Dover Patrol drifter HMS Roburn, saw that the submarine had became trapped in anti-submarine nets, and surfaced which brought tribal class destroyers HMS Ghurkha & HMS Maori to the scene who opened fire on the submarine and then went alongside and with cutlasses and small arms the navy boarded the submarine. Before abandoning the U-8 crew had opened up the seacocks, all the U-8 were taken onboard HMS Arrogant. The submarine was taken in tow but sank off the southern end of the Varne bank. The wreck of the German submarine U-8 is one of the favorite dives of Canterbury's British Sub-Aqua Club and wreck divers.

In 2014 two divers from Sandgate in Kent pleaded guilty at Southampton Magistrates’ Court to the offence relating to sections 236 and 237 of the Merchant Shipping Act 1995, and were fined £62,500 for taking historical artifacts worth more than £250,000 from sunken vessels without declaring them. Among the plundered artifacts were items from the German Submarines UC-64, UB-40 and U-8.

A propeller from U-8 had been removed illegally from the sunken wreckage by divers and found by Kent police in a Sandgate property in June 2014 apparently fashioned into a coffee table, was returned to the German Navy at a ceremony aboard Karlsruhe in Portsmouth Naval Base in June 2015.