The U 73 submarine

Construction and technical characteristics

Uboot Dampfer

A propaganda post card which was given as a token of appreciation to participants in the fund raising campaign for supporting the submarine warfare of the First World War. (KFB Collection).

The German Admiralty (Admiralstab) commissioned in early 1915 the building of 10 extended range minelaying submarines, which were intended to be integrated to the offshore fleet, the so-called Hochseeflotte. These type of submarines, although often referred to as U71 class because of the first submarine code name of the series, were widely known as the UE 1 class. The production series of this class, included sub names from U 71 up to U 80. These 10 sub’s were built by two different shipyards, Vulcan in Hamburg and the Imperial Shipyard (Kaiserliche Werft) in Danzig, the first one building eight and the second the other two. One of the two, sub U 73, with production S/N 29, was to play an important role in the conduct of naval warfare in the Mediterranean, as her commander, Gustav Siess, with a record sinking of 56 ships totaling 188,895GRT, ranked sixth on the list of the most successful submarine captains of the First World War.

The U 73 was launched on 16th June 1915 and had the following characteristics:


The U 73 at Cattaro during spring 1916. (Copyright © Internationales Maritimes Museum Hamburg).

  • Displacement: 755 tons (surfaced), 832 t. (submerged), 980 t. (total)
  • Length: 56.80 meters (total), 46.66 m. pressure hull
  • Beam: 5.90 meters (total), 5.00 m. pressure hull
  • Draft: 4.86 meters
  • Height: 8.25 meters
  • Engines: Two Körting diesels, two electric motors
  • Horsepower: 900 hp (surfaced), 900 hp (submerged)
  • Nominal speed: 10.6 knots (surfaced), 7.9 knots (submerged)
  • Range: 7,880 nautical miles at 7 knots (surfaced), 83 nautical miles at 4 knots (submerged)
  • Torpedoes: Four
  • Torpedo tubes: Two external 50.8 cm (bow, stern)
  • Mines: 34
  • Deck Gun: One 88 cm
  • Crew: 32 men
  • Maximum depth: Approximately 50 meters

Although indicative submarine components predispose us to understand it as a successful engineering exercise of shipbuilding and construction of the times, reality was different. According to the report and descriptions from main eyewitnesses, as Martin Niemöller,-who served as navigator in the U 73 between 22nd February 1916 to January 1917 and has recorded his experiences in a book titled, Vom U-Boot zur Kanzel (From the Submarine to the Pulpit), since during the post-war years he became a clergyman,- we learn that the sub was not only slow on the surface, barely achieving 9.6 knots, but while submersed her speed could not exceed 4 knots and such was reached only for short periods. Also, the dive process lasted two minutes while the surfacing procedure was quite lengthy. The biggest problems however involved the diesel engines, which aside from being inadequate, required constant adjustments and often broke down. There were various other technical shortcomings, as the occasional erroneous gyrocompass readings, which made-up a long list of problems for the sub. Rightly then one could wonder how this submarine has been so successful? Perhaps the answer to this is that most successes of U 73 were caused by her mines, in addition of course to the remarkable administrative skills of her Commander, Gustav Siess.

Kapitänleutnant Gustav Siess

G. Siess

Gustav Siess, Commander of U 73, still ranks among the "Aces" of submarine warfare. In 1918 after his decoration with the Pour le Mérite medal, his full size picture was displayed at the downtown shop, "Foto Dürkopp". By this way the City of Hamburg honored its hero, the first to earn the Pour le Mérite highest distincton. (Foto Dürkopp - Hamburg).

Kapitänleutnant Gustav Siess was born in Hamburg on 11 December 1883 and enlisted in the German Imperial Navy (as Crew 04/1902, Deutsche Kaiserliche Kriegsmarine) in 1902. The break-out of the war found him as a commander of a V1 class torpedo boat. Shortly after serving as commander of a V 3 class torpedo boat, Gustav Siess requested to be transferred to submarines where after a three month training period, was appointed Commander of submarine U 41. Shortly after, because of his special skills, was appointed in August 1915 as submarine commander of the U 73, shortly before the vessel was delivered for her first sea trials(9.10.1915) scheduled to take place in the Baltic Sea at the submarine base of Kiel.

Gustav Siess and his submarine managed to sink the largest tonnage of ships in his career, including  S/S Burdigala and HMHS Britannic. During his Command of U 73 (October 1915 – April 1917), he sunk 17 merchant marine ships (a total of 96,742 GRT) and two warships, the British Russle and the Russian PERESVYET. Gustav Siess, aside from U 73,  also commanded the subs U 33 and U 65. For his successful actions was decorated with the Iron Cross of the first and second order and the medal Pour le Mérite, in April 1918.
After the First World War, during the period known as the Weimarer Republik, Gustav Siess established a trading company by the name “Siess, von Loë & Co”. In 1935, after pilot training at age 53, rejoined the ranks of the military with the rank of Major General (Generalmajor) and was responsible for logistics at the Ministry of Aviation (Luftwaffe) in Berlin. In 1944, after a severe illness, left the ranks of the German Air Force later to be arrested in 1945, by the Russian Red Army. Sentenced to 25 years in a Russian detention camp and released ten years later, in 1955, when he returned to Hamburg. Gustav Siess died after a full life in the city of his birth on 14 October 1970, at age 87.

Minefield Nr. 32


Excerpt from p. 38 of Martin Niemöller's book, navigator of U 73, titled "Vom U-Boot zur Kanzel". In this section he describes the laying of minefield Nr. 32 along the Kea island northern coast. (KFB Collection).

Although the career of U 73 was rich in achievements, -in our website we have compiled a chronology of events from January 1915 until September 1917 – a specific fact draws our interest as it concerns us particularly. It pertains to the laying of minefield Nr. 32 in the Kea Channel on the 28th October 1916, which resulted in the sinking of the large ships S/S Burdigala and HMHS Britannic. Preferring to quote accounts from primary sources, we convey here below the story from an eyewitnesses, the Navigator Martin Niemöller, as recorded in his book “Vom U-Boot zur Kanzel”.

“First encounter: a small modern British cruiser. But we did not manage to reach close enough within torpedoing range. During the next day, although we remain at the same position, we are not lucky enough as there is no activity near us. During the night we head north and enter in the Saronic Gulf. By dawn, after several encounters with cruisers during the night and repeated evasive dives, we are positioned in front of Fleves little island northeast of Aegina. During the morning here develops heavy shipping traffic, which is overseen by a protective French destroyer not far from us. The weather is rough and it is difficult to maintain the U 73 at periscope level. At noon two minefields will be positioned east and west of the small island,  intercepting the shipping route and then will move south to the Kea Channel. In the evening while surfaced we head off the coast of Evia, in the Petali Gulf while we recharge the batteries [of the sub]. We do not have a quiet night though as we are forced to dive three times to avoid encounters with by-passing destroyers.  Near the Kea Channel we see during the night two hospital ships sailing under full lights, heading in a southerly direction. Some other ships, which were sailing almost without lights, we could not detect.

The Otranto barrier,-consisting of fixed anti-submarine nets, a flotilla of 160 small fishing boats dragging nets and constant patrols by naval vessels,-was set-up in autumn 1915 and remained active until the end of the war. The purpose of the barrier spanning across the 40 miles of narrows between Italy and Albania, was to obstruct passages of both German and Austrian-Hungarian submarines and to prevent the exiting of Austrian-Hungarian Navy (KuK Marine) ships from the Adriatic. It was the barrier which all Deutsche U-Flotille Pola subs had to negotiate, among them the U 73. (KFB Collection).

Early in the morning at five we dive and head toward the Kea Channel seeking a suitable spot to lay our minefield. It was not difficult to find, as all ships were passing near the coast of Kea. At the same time we discovered with dismay that within the shipping lanes, several minesweepers were sailing in formation and active with their detection equipment deployed. So they await our visit. Between eight and nine o’clock in the morning with luck we deploy two minefields, each consisting of six mines, in front of the Kea shores and remain in position until the afternoon waiting to see if something will happen, so that upon a successful hit we could be in a position to finish off the stricken ship. Around eleven a large steamer, listing heavily on one side, passes near the minefield within a quarter of an hour with a southerly heading, but we are unable to get close to her. Did she strike a mine? We do not know!

During the day even more ships pass-by, especially hospital ships which are distinguished by their white color and green line. Either a major epidemic has spread in the French camps of Thessaloniki, or they use the protection of the Red Cross to transport safely troops and war materiel! Late in the afternoon we abandon our position and submerged head northeast through the Cavo Doro strait, seeking quiet waters to pass the night as undisturbed as possible and to recharge the sub’s batteries”.

The end of U 73

The U 73 submarine remained active throughout the war’s duration. Besides Gustav Siess, other officers who served as Commanders were: Kapitanleutnant Ernst von Voigt (22 May 1917 – 15 January 1918), Kapitanleutnant Karl Meusel (16 January 1918 – 15 June 1918), Kapitanleutnant Carl Bünte (16 June 1918 — 14 July 1918) and Kapitanleutnant Fritz Saupe (15 July 1918 – October 30, 1918). At the end of the war in October 1918, Theodor Pullen,Commander of the German submarine fleet at Pola, issued orders for all subs in the Mediterranean Sea to return to their base for refueling and food supplies, before commencing their long sail back to Kiel Naval Base. Whichever subs were deemed incapable for making this long and dangerous journey, were scuttled.  Among those was U 73, dynamited in Pola on 30 October 1918.

Copyright © 2009 by D. Galon and the S/S Burdigala Project Team

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