U51 class (1915)

Germany: SM U51 to U-56 (1915-16)

The U51 class U-Boats were essentially a repeat of the U41, the last, modified boat of the U31 class by Germaniawerft. They were the first double-hull U-Boats of this type, part of the mobilization program and were internally called the Ms type. Six were built, laid down in the summer of 1914 and launched from November 1915 to April 1916. Most improvements focused on their diving time, down to a minute and 45 seconds, like for the rival U47 from Dantzig NyD, but unlike the latter which had a brand-new type of streamlined hull, the U51 class stuck to the standard design. Thet were gun deck variations over time. These were for some (U52 and U53) quite successful (100+ ships sunk, 400,000 GRT inc. a battleship and a cruiser) and most survived the war. U53, 53 and 55 were attributed to the allies postwar, the latter to Japan, which used her for years as O3.

Design of the U51 class:

Development

There was some hesitation before dedicating a fully fledge post on these, as there is not much to go with these boats. They really were a follow-up of the U41, the last boat of the U31 class by Germaniawerft. To be in context, back in 1913-14, not only U-Boats were seen a bit more seriously (after their 1914 successes, the opinion changed completely), and both Germaniawerft in Kiel and Kaiserliches Werft in Dantzig, both being state-sponsored naval yards, were de facto rivals in submarine construction. Orders alternated between the two.

Danzig unveiled the U47 before Germaniawerft, and so the latter stuck to their traditional hull design, double-hulled, but starting not with the U31 as base for improvement, but the well modified U41, last in class. U41 was launched in October 1914. The main goal was to revise the management of the ballasts and water scoops to reach a better diving time, at least the same declared by Danzig NyD with their U43 series. Both were ordered as part of the same naval program and the goal of Danzig was not only to improve the diving time, but also range and underwater performances, albeit in that case, this ended inferior to the U51s (see later).
The U51 class comprised six boats, instead of eight for the more promising U43 class, part of the mobilization program. They were launched from late 1915 to early 1916 and completed in 1916, when the U-Boat was already in full swing and the prospects for the surface fleet was lower after Jutland, despite a propaganda victory. However by that stage, the allies learned from their errors, and became way better at ASW tactics.

Hull and general design

From U19 to U53 the Germaniawerft design was very conservative, which just incremental improvements
The U51 class displaced 715 tonnes surfaced (704 long tons), 902 tonnes submerged (888 long tons), and 1060 tonnes total, submerged and fully loaded. The overall length of the hull was 62,20 meters (213 ft 11 in), so like the U23/U19 with a pressure hull 52,51 meters long (172 ft 3 in), an overall beam of 6,44 meters (21 ft 2 in) while the pressure hull was 4,18 meters (13 ft 9 in) in diameter. The draught was now 3,64 meters (11 ft 11 in), a bit more of the 3.6 meters or 11 ft 10 inches of the U31 class. The total height from the keel to the top of the conning tower was 7,82 meters (25 ft 8 in), not comprising the periscopes or wireless radio masts. It seems the conning tower was larger and roomier, and the outer hull was more rounded, albeit the central deck was still there. She was the last featuring this classic design.

Power plant of the U51 class

It was classic, with two bronze fixed-pitch 1.7 meters diameter propeller shafts driven by two MAN diesels for a total of 2,400 PS (1,765 kW; 2,367 shp.) surfaced, and two SSW-Elektromotor electric motors for 1,200 PS (883 kW; 1,184 shp) submerged. The electric engines were from Siemens-Schuckertwerke (founded 1903). This made for a top speed of 17.1 knots (31.7 km/h; 19.7 mph) surfaced and 9.1 knots (16.9 km/h; 10.5 mph) submerged. To compare, the rival U43 series were less powerful at 2000/1200 shp. and reached 15.2 knots surfaced, and 5 knots submerged, so a dramatically lower set of performances. However, the U51 had a range of 9,400 nmi (17,400 km; 10,800 mi) at 8 knots (15 km/h; 9.2 mph) surfaced and 55 nmi (102 km; 63 mi) at 5 knots (9.3 km/h; 5.8 mph) submerged, better than the 8100 nm/51 nm figures of the U43, so it ended superior apart for having less torpedo tubes. Test depth was still 50 m (164 ft 1 in), crush depth was more than double that.

Armament

There were two changes for the U51 compared to previous designs U-19 to U41: Still four torpedo tubes, two in the bow, two in the stern, but enough space was managed to store four spare torpedoes instead of two as on prior designs, so eight in all, counting the four preloaded in the tubes. This was still less than the four bow tubes sported by the U43 class. The other change was the artillery, with a new mobilization standard asking for two 8,8 cm deck guns, one forward and one aft of the conning tower. However as for other types, later in the war, mostly in 1917, some 8,8 cm were replaced by a 1.05 cm main gun, sometimes one 105mm forward and a 88mm aft, or a single 105mm and nothing else.

Torpedo Tubes

Germany started by equipping its torpedo boats and early U-Boats of the 1890s with the 35cm (14 in) C35/91 and C35/91GA, then 45cm (17.7 in) C45/91 Br, C45/91S, C/03 and C/03 D were reserved for surface ships, and the C/06 and C/06 D for U-Boats from U3 onwards. They stayed standard before the introduction of the 50 cm. The initial model was reserved for surface ships. This was the (19.7″) G/6 and G/6D which used either the Decahydronaphthalene (Decalin) or Kerosene Wet-Heater.

U23 was the first to introduce the new and famous G7 (entering service in 1913), repeated by the U27 class and follow-up U31 class. Still, there were important stocks of G/6, and it’s possible they were used for training or tests. The Kerosene powered G/6D was considered too “temperamental” for submarine use indeed. The G/6 was developed from 1908 and entered service in 1911. The Royal Navy was slower on this chapter, only introducing the 21″ (53.3 cm) Marks II, II* and II** for submarine use from 1914 onwards. The four 500 mm (19.7 inches) torpedo tubes could be reloaded from above via the larger hatches going through the outer upper hull.

G/6 specs

Weight unknown, 236 in (6.000 m) length overall
Warhead 353 lbs. (160 kg) TNT/Hexanitrodiphenylamin (Hexanite) mixture
Range/Speed 2,410 yards (2,200 m) at 35 knots or 5,470 yards (5,000 m) at 27 knots
Power: Decahydronaphthalene (Decalin) Wet-Heater
More on navweaps

G7 Torpedo

The G7 was designed in 1910 and entered service in 1913. Originally designed for surface ships, but in 1917 it started to be used on U-boats.
Specs:
Weight: 3,009 lbs. (1,365 kg)
Overall Length: 276 in (7,020 m)
Explosive Charge: 430 lbs. (195 kg) Hexanite warhead
Range/Speed settings: 4,370 yards (4,000 m)/37 knots and 10,170 yards (9,300 m)/27 knots
Power: Decahydronaphthalene (Decalin) Wet-Heater

8.8 cm Schnelladekanone Länge 30 naval deck gun

For the U19 onwards, the classic 3,7 cm or 5cm deck guns were ditched out and as U19 was considered large and stable enough to have a larger gun installed and a single 88mm 27 calibre TK L/30 C/08 deck gun was installed forward. For this the deck was reinforced but no sponsons extensions appeared seemingly on photos.

In 1916, after captains reported this gun still weak, notably to scuttle a boarded ship or engage an armed trawler. They spent way too much time sinking their prey, which called for enemy reinforcements. Thus, all four boats had a second 8,8 cm deck gun installed aft, making two. U19 was the first U-Boat class with two guns, fore and aft. This was repeated for the U23 and U27 classes in wartime. U30 exchanged both guns for a single 10.5 cm/43 TK L/45 C/16 deck gun in 1918. The 8.8 cm became the standard go-to gun for all U-Boats built afterwards, until the U87 class (launched 1916), generally two for oceanic boats, one for minelayers and for later coastal subs. They accounted for many of their preys.

The 8.8 cm SK L/30 gun used the Krupp horizontal sliding block, or “wedge” and the submarine deck version was on either a retractable or fixed pivot mount. The Krupp mount retracted vertically through a hatch, and the Erhardt version folded down onto the ship’s deck. They avoided underwater drag and turbulences. It seems U19 class had the Ubts.L of the second type.
The 8.8 cm SK L/30 was a widely used naval gun on World War I pre-dreadnoughts, cruisers, coastal defence ships, avisos, submarines and torpedo boats in both casemates and turrets as well.
This calibre became so ubiquitous in the German Navy it was still a favourite for WW2 U-Boats as well starting with the Type VII. Read more

Specs 8.8 cm SK L/30 on Ubts.L mount

Weight: 644 kilograms (1,420 lb)
Overall length: 2.64 meters (8 ft 8 in).
Breech: Krupp horizontal sliding block
Shell: fixed 7 kg (15 lb) cal 88 mm (3.5 in)
Elevation: -10° to +30°
Rate of fire: 15 RPM
Muzzle velocity: 590 m/s (1,900 ft/s)
Maximum firing range: 7,3 km (8,000 yd) at 20° or 10,5 km (11,480 yards) at 30°

10.5 cm SK L/45 naval gun (1916)

In late 1917 and 1918, some boats traded their two 8,8cm deck guns (or single one) for a single 105mm deck gun with 300 rounds. The crew rose to 46-48 men less four officers, now with a proper gunnery officer.
Built by Meddinghaus, this heavy deck gun was designed specially for deck use, low, with many sensible elements protected from corrosion.

Specs 10.5 cm SK L/45

1,450 kg (3,200 lb), 4.725 m (15 ft 6.0 in), 6.8 mm (0.27 in) wide.
Shell 10.5 cm (4.1 in) 25.5 kg (56 lb) fixed Brass Casing 17.4 kg (38 lb)
Breech: Horizontal sliding-block, MPL C/06: -10° to +30° mount
Rate of fire: 15 RPM
Muzzle velocity 710 m/s (2,300 ft/s)
Effective range 12,700 m (41,700 ft) at 30°

⚙ U51 specifications
Displacement	715 t (704 long tons) surfaced, 902 t (888 long tons) submerged
Dimensions	65.2 x 6.44 x 3.64m (213 ft 11 in x 21 ft 2 in x 13 ft 2 in)
Propulsion	2 shafts MAN diesel engines 2,400 hp, 2 × twin Modyn electric motors 1,200 PS
Speed	17.1 knots surfaced, 9.1 knots submerged
Range	9,400 nmi at 8 kn surfaced, 55 nmi at 5 knots submerged
Armament	4× 50cm TTs (2 bow, 2 stern, 7 torpedoes), 2x 8.8 cm SK L/30 gun
Max depth	50 m (160 ft)
Crew	4 officers + 32 men

Career of the U43 class

U51

U51 was ordered 23 August 1914 from Germaniawerft, Kiel like all her sisters, with the Yard number 233. She was laid down on 19 December 1914, launched on 25 November 1915 and completed at Kiel about March 1916. She started trials at the Kiel School and 1st flotilla until the end of April, and for her first mission proceeded to Heligoland. British Naval Intel, Room 40 monitored and recorded her activities when she was assigned to the 2nd Half Flotilla under her first commander in May 1916, Kptlt. Walter Rumpel. She was on patrol in the North Sea between 2 May and 6 May 1916, sailing to Hanstholm with SM U-70, escorted by two Zeppelins which reported from their vantage point, all naval activities. The patrol was uneventful. She was back in the North Sea between 16 May and 3 June 1916, taking part in affect to the Battle of Jutland. She fired two torpedoes at the HMS Warspite but missed.
On 14 July, British submarine HMS H5 spotted her while she was leaving the Ems. This spot was well known and despite the danger of German patrol ships, she sailed there laying in ambush and this paid off. She landed at least one or two torpedoes on U-51. She sank with the loss of 34 men, with four survivors rescued, likely in the CT when it happened, as U51 was surface running when it happened. Her wreck was raised and broken up in 1968 as a potential navigation hazard.

U52

U-52 was launched on December 8, 1915, at the Germaniawerft shipyard in Kiel and commissioned on March 16, 1916. The submarine’s commanders were, in chronological order, Hans Walther, Johannes Spieß, Siegfried Claaßen, Waldemar Haumann, and Franz Krapohl.
During the War, U-52 conducted only four patrols in the eastern North Atlantic (until 25 May 1916 I Flotilla, until 24 Dec 1916 II Flotilla) but also the Mediterranean (until 27 April 1917 Pola Flotilla). She became one of the most successful in class with a total of 28 merchant ships of the Entente and neutral states sunk, which represented some 71,225 GRT. She also successfully sank warships, such as the 5,400 GRT British light cruiser HMS Nottingham, off the coast of Scotland on August 19, 1916. On November 25, 1916, U-52 did even better, sinking the 12,750-ton French battleship Suffren near Lisbon. All her kills were under KptLt. Hans Walther.
At the end of October 1917, as part of the II. Flotilla, there was a crippling accident: A torpedo exploded in her stern torpedo room near Kiel while she was moored at the entrance to the Kaiser Wilhelm Canal. It is not known how it happened, but fortunately “only” six crew members were killed in the accident. A memorial commemorating their names was erected postwar at the Kiel North Cemetery. On October 31, 1917, she was raised and repaired. She remained in service with the same unit under Siegfried Claaßen, Waldemar Haumann, apparently as a training boat, and by November 21, 1918 under Kptlt. Franz Krapohl, U-52 was awarded to the United Kingdom as reparation, exposed to the public for some time and scrapped in Swansea in 1922. Detail of the tally.

U53

u53
U53 in Newport, Rhode Island. The first transatlantic crossing by a (modified) U-Boat, preceding the Deutschland. She was also the most successful U-Boat in the class.
U-53 was launched on 1 February 1916 at the Germaniawerft shipyard in Kiel and commissioned on 22 April 1916. The submarine’s commanders were Hans Rose (22 April 1916 – 17 August 1918) and Otto von Schrader (18 August 1918 – 29 November 1918). During the War, U-53 made 13 combat patrols in the North Atlantic, plus a single transatlantic patrol, sinking total of 85 merchant ship s(Uboat.net states 87) with a total tonnage of 217,508 GRT (uboat.net 224,314t) and damaged ten ships (46,339 tons) making her the most successful in class, and one the most successful U-Boat in the war. The tally included a US destroyer (see later). Measured by gross register tons sunk alone, she ranked fifth in World War I.
She notably sank two tankers, and a passenger liner, the 10,400 tonnes Devonian.
U 53 was the first U-boat to cross the Atlantic. This exceptional patrol started in September and ended in October 1916, intended to secure a route for German merchant submarines such as the brand-new Deutschland intended to break the blockade and bring back home critical material purchased in the US. U53 was successful, demonstrated also that in case of a war with the US, this opened a brand-new hunting ground.

This gave an idea to the high command and led to the construction of the “U-Kreuzer” specifically designed for transatlantic combat. Previously, U 53 was equipped with several submersible tanks at the Germania shipyard, usable as fuel bunkers for this long voyage. Lieutenant Commander Rose performed quite a feat when he entered Newport in Rhode Island and stayed there for 2 hours on October 7, 1916. She berthed, the crew left, and US Naval personnel were invited to visit her. On October 8, 1916, Rose started a prize rule combat patrol just outside US territorial waters, where merchant vessels to Britain were completely unescorted. This allowed her to stop seven and sink five ships in quick succession, single-handily prefiguring the first “second happy time” for U-Boats just 20 years prior.
On February 3, 1917, U-53 sank the US merchant ship Housatonic, 20 miles south of Bishop Rock and if there were no casualties, this further deteriorated relations between Germany and the United States. On December 6, now with the US at war, she sank the US destroyer Jacob Jones southwest of Bishop Rock, with a hit from 2,700 meters. 64 men went down and this was the first loss US Navy destroyer lost to submarine action in any war. Detail of the tally

U54

U54 was ordered from Germaniawerft, Kiel (Werk 236) on 23 August 1914 as a mob type. She was laid down on 18 March 1915, launched on 22 Feb 1916 and commissioned on 25 May 1916.
Her first commander until 19 May 1917 was Kptlt. Freiherr Volkhard von Bothmer. Her was succeeded until 22 March 1918 by Kptlt. Kurt Heeseler and until the end of the war by Oblt. Helmut von Ruckteschell for a total of 12 patrols, all in the same II. Flotilla, sinking 26 ships for a total of 66,713 tons, four damaged for 17,847 tons and a 1,290 tons warship, the Q-ship HMS Starmount. Another case of a hunter that became a prey as the latter were dedicated ship made to fool and gun down a U-Boat at close range under prize rules. However, in 1918, the latter no longer applied as it was unrestricted warfare. All Q-ships were at risks and mostly carried out patrols. The largest ship sank was the Italian tanker San Lorenzo, 9,607 GRT.
She surrendered on 24 November 1918 and was allocated as war reparation to Italy, which had it broken up at Taranto in May 1919.
Details of the tally

U55

U55 after her arrival to Yokosuka, later O3. Note, she combined a 105 mm forward and 88mm aft.
U55 was ordered at Germaniawerft, Kiel (Werk 237) on 23 August 1914, laid down on 28 Dec 1914, launched on 18 March 1916 and commissioned on 8 June 1916 under commander Kptlt. Wilhelm Werner (awarded a Pour le Mérite) until 9 August 1918 in the II Flotilla. She was quite successful with 14 patrols, sinking 64 ships for a total of 133,742 tons, damaged seven for 26,161 tons and took two ships as prize for 3,466 tons.
Her largest kill were the 8,153 tonnes Passenger steamer Ausonia and more so, the 13,603t Passenger steamer Carpathia, a Cunard ship made famous for saving most of the RMS Titanic‘s survivors.

RMS Carpathia sinking, photo taken from the CT of U55 as she approached the lifeboats.
On 15 July 1918, Carpathia departed from Liverpool in a convoy bound for Boston with 57 passengers (36 saloon, 21 steerage) and 166 crew on a zig-zag course and with escort, but the latter left the convoy on 17 July while her convoy was split, and she continued west along with six other ships, largest in the convoy she became the commodore ship. At 9:15 a.m., while off the Southwest Approaches, spotters sighted a torpedo coming on her port side. The engines were immediately ordered full-astern, helm hard-a-starboard, but this was too late. The torpedo hit near the No. 3 hatch, followed by a second penetrating the engine room, killing 3 firemen, 2 trimmers, disabling her completely as her electrical gear, wireless radio. Captain William Prothero signalled other ships in the convoy to send out wireless messages by flag and used rockets to attract attention of nearby patrol boats while the remaining ships steamed away at full speed.

She later started to settle by the head, listing to port, and he gave order to abandon ship with all passengers and crew boarding 11 lifeboats making for a total of 218 survivors out of 223. However, as she sank there was still on boars the chief officer, first and second officers and gunners remaining at post. They threw overboard the confidential books and documents before jumping at sea, just when U-55 surfaced and fired a third torpedo which entered the gunner’s rooms, causing a massive explosion that sent Carpathia down quicker, yet still 1 hour and 45 minutes after the first hit. U55 then d approached the lifeboats to enquire about the ship and provide potential help and direction, when the Azalea-class sloop HMS Snowdrop was spotted rushing forward, starting firing, so U55 quickly submerged and escaped. She joined other ships in class, Ascania, Ausonia, Dwinsk and Valentia, leaving only five Cunarders afloat.

U55 was later versed into training with caretaker captains, Kptlt. Alexander Weiß and Oblt. Hans Friedrich. On 26 November 1918 she was surrendered, and allocated to Japan. In Japanese service she became O3, was carefully studied and remained in limited service (semi-operational, she was mostly making trial runs) in 1920-1921. She was partially dismantled at Sasebo Navy Yard in March-June 1921 but by 1923, briefly re-commissioned as Auxiliary Vessel No. 2538 in a non-operational state.
Tally of U55

U56

Allegedly U56 in Santander, Spain, in 1916, US NARA archives – War Department. Army War College. Historical Section. World War I Branch. ca. 1918-ca. 1948
U56 was ordered from Germaniawerft, Kiel (Werk 238) on 23 August 1914, laid down on 28 Dec 1914 and launched on 18 April 1916, commissioned on 23 June 1916 so aft the Battle of Jutland.
Until 3 November 1916 she was under command of Kptlt. Hermann Lorenz as part of the II Flotilla and only saw a single patrol in the Baltic sea, sinking 5 ships for 5,701 tons. On 3 November 1916 she was presumably lost, never returned home and presumed missing, with all hands lost. Prior to her sinking by the Russian destroyer Grozovoi off Khorne Island, Norway (near Vardö). There are conflicting stories, as some reported her surviving the gunfire attack and diving. Before that, U 56 last prize was the 1,136 GRT Norwegian merchant merchantman, Ivanhoe on 1st November. She rescued the crew, and landed them ashore at 07:45 on November 3 at Lodsvik. They latter saw the action and their story matched the Russian report.
Tally of U56