Prior to the more advanced classes of German U-boats to see service in World War 2 (1939-1945), the German government funded its first post-World War 1 submarine project which produced the Type I-class. The class consisted of just two boats - U-25 and U-26 - but lay the foundation for the classes that followed and served to gain command of Atlantic waters for the German Kriegsmarine (Navy). Both led relatively short wartime service lives and both were lost in action - U-25 sunk by naval mine and U-26 scuttled by her crew after depth charge damage.
Submarines of the period were constructed along two general performance lines - coastal and ocean-going. The Type I represented the latter which showcased an all-new set of challenges for engineers. The class was influenced by the Spanish Type E-1 which provided the deep sea capabilities the Kriegsmarine sought. Design of the new class was handled by Ingenieurskantoor voor Scheepsbouw with construction through Deschimag at its Bremen shipyard. U-25 was laid down on June 28th, 1935, launched on February 14th, 1936 and commissioned on April 6th, 1936. U-26 was laid down on August 1st, 1935, launched on March 14th, 1936 and commissioned on May 6th, 1936. In their early use, both boats served as chief propaganda tools for the Nazi Party. In addition to their political value at the time, the vessels provided valuable instruction platforms for a new generation of German submariners.
As built, the class displaced 710 tons under standard load and featured a length of 237 feet, 6 inches, a beam of 20 feet, 4 inches and a draught of 14 feet. The boats were given typical design profiles of the time with flat top decks, a boat-like bow shape and bulged sides. The conning tower was held near amidships to provide commanding views about the boat. A deck gun to counter surface ships was fitted ahead of the tower while an anti-aircraft weapon was fitted aft of the tower along an integral platform. Power was served through 2 x MAN M8V40-46 series 8-cylinder diesel engines providing up to 3,080 horsepower to 2 x shafts. These powered the vessel while on the surface. Submerged propulsion came through 2 x BBC GG UB720/8 series electric motors developing 1,000 shaft horsepower. Consistent with other submarines of the period, the Type I was required to surface to recharge its batteries and oxygen while releasing any built-up dangerous gasses. The propulsion system allowed for a top surfaced speed of 18 knots with a top submerged speed of 8 knots. Range was limited to 7,900 nautical miles on the surface and 78 nautical miles submerged. The vessel could reach depths down to 200 meters. All told, the Type I supported a typical crew of 43 personnel made up of 39 sailors and 4 officers.
The class was designed from the outset as attack submarines which could also lay naval minefields. As such, the boats carried six total 533mm (21") torpedo tubes with four mounted at the bow and two facing the stern. This provided the captain with two engagement angles not requiring his boat to be turned completed around to fire at targets aft. Fourteen total torpedo reloads were carried. As a minelayer, the submarine was cleared to carry some 28 TMA type naval mines. Surface threats were countered through the 105mm SK C/32 caliber deck gun which was fully traversable on its deck mounting. Similarly, aerial threats were dealt with through the 1 x 20mm anti-aircraft cannon installation. The weapons required the crew to be present (and exposed) along the deck and conning tower of the boat (common practice with most submarines of the period).
When German forces invaded neighboring Poland on September 1st, 1939, World War 2 officially began and the two boats were pressed into combat service. While these were generally acceptable submarine designs, their capabilities proved them slow divers with cumbersome controlling aspects though they nonetheless managed quite successful career during their short period of service.
U-25 managed five war patrols during her tenure of the seas and was credited with sinking eight enemy vessels to the tune of 50,255 tons from the period of October 1939 to June 1940. Her crew also managed to damage at least one ship. Her end came on August 1st, 1940 when, under a mine-laying excursion off the coast of Norway, she herself fell victim to a British naval minefield in turn with the subsequent damage proving so severe that the boat was lost with all hands (49).
U-26 covered six total war patrols and sunk eleven enemy vessels while damaging at least one other. Like U-25, U-26 was used in mine-laying missions to help control vital waterways. Her operational tenure began in August of 1939 and ended on July 1st, 1940 after incurring heavy damage from British depth charges. The boat was forced to surface which led to the crew (48) scuttling U-26 and surrendering. U-26 sunk 49,185 tons during her raiding forays.
Such ended the service records of the Type I class of German U-boats.