German submarine U - 4 ( 1935 ) German submarine " U - 4 " was a Type IIA U - boat of Nazi Germany ' s " Kriegsmarine " before and during World War II . She was one of the longest lasting German submarines of the period , primarily since half of her time was spent on training duties in the Baltic Sea . Commissioned on 17 August 1935 , she was one of the first batch of Type IIA boats constructed following the Anglo - German Naval Agreement that repealed the terms of the Treaty of Versailles which ended the First World War and stated that Germany was not permitted to possess submarines . Built at the Deutsche Werke in Kiel as yard number 239 , she was a highly sought after command before the outbreak of the Second World War in 1939 . Once the war had begun however , she rapidly became obsolete . Before she was superseded , she carried out four combat patrols , mainly in support of the Norwegian campaign . Design . German Type II submarine s were based on the . " U - 4 " had a displacement of when at the surface and while submerged . Officially , the standard tonnage was , however . The U - boat had a total length of , a pressure hull length of , a beam of , a height of , and a draught of . The submarine was powered by two MWM RS 127 S four - stroke , six - cylinder diesel engines of for cruising , two Siemens - Schuckert PG VV 322 / 36 double - acting electric motors producing a total of for use while submerged . She had two shafts and two propellers . The boat was capable of operating at depths of up to . The submarine had a maximum surface speed of and a maximum submerged speed of . When submerged , the boat could operate for at ; when surfaced , she could travel at . " U - 4 " was fitted with three torpedo tube s at the bow , five torpedo es or up to twelve Type A torpedo mines , and a anti - aircraft gun . The boat had a complement of 25 . War patrols . 1st and 2nd patrols . " U - 4 " departed Wilhelmshaven for her first patrol on 4 September 1939 , in the aftermath of the declaration of war . Given her small size , she only covered the area to the south of Norway and into the North Sea west of Denmark and along the Dutch coast , and returned unsuccessful on 14 September . A second patrol later in the month yielded greater dividends , when she spotted three neutral vessels heading to Britain through the North Sea and sank them on consecutive days ; the " Martti Ragnar " on the 22nd , the " Walma " on the 23rd and the " Gertrud Bratt " on the 24th . 3rd and 4th patrols . Her later two patrols were both in support of the German invasion of Norway . It was during this operation that she was able to sink the British submarine . The engagement was a lengthy one , as " U - 4 " was a small coastal craft with poor endurance . When " Thistle " attacked and missed " U - 4 " on 9 April , it gave the German submarine a chance to evade and hunt her attacker , finally catching and sinking the British vessel as she recharged her batteries on the surface a day later . The Baltic . Once Norway was subdued , it became increasingly obvious that " U - 4 " and her sisters were not capable of either outfighting or outrunning enemy craft , neither did they possess the range and endurance necessary to have a major impact on Allied shipping . In response , on 1 July 1940 , these boats were relegated to the 21st U - boat Flotilla , and served until 1944 as training craft in the Baltic Sea . Although some of her sisters saw action later against the Soviets , " U - 4 " did not , eventually being retired from all service at Gotenhafen ( now known as Gdynia in Poland ) , on 1 August 1944 , and then scrapped for parts sometime in 1945 .