U 139 class U-Boats (1917)

Germany U-Kreuzer U 139, U-140, U-141

The U 151 we already saw were civilian cargo submarines of 1916. Completed in the summer of 1916 for the Nord Deustchler Lloyd to trade with the US, they created quite a splash in the Kaiserliches Marine’s top brass. It proved such long range concept was valid and the answer was two-prone: Requisition these new boats and order more, then design a new, proper military submarine, integrating the most interesting features of the SS Deutschland, Bremen and Oldenburg. The final result was longer but narrower, faster, and carrying the same amazing four-deck gun armament but six torpedo tubes instead of two, and a large provision of 24 torpedoes. Only three were built due to their large cost and to test the waters for the U-142 class (Project 46a), a large scale construction project of 37 boats from four yards (three completed before V-Day).

Development of Project 46

The U-46 were developed as a proper military “U-Kreuzer” or cruiser submarines from the get-go. The idea was not absent for the Kaiserliches marine’s staff, as such proposals were already made in 1915, albeit in the idea to hunt down British convoy in other places than just the Atlantic and Mediterranean. It was suspected indeed that the Indian Ocean was vital to British interests. Since it was out of question of crossing the Suez canal, the only solution for any U-Boat to get there was through the Cape of Good Hope. An enormous distance implying, without any bases there, either a refuelling ship operating from a neutral port in the area, or massive reserved of fuel oil. Such prospect led to design Project 50 later, a steam-powered, very long range submarine. But such idea was complicated to turn into reality and none was ever built, even though plans were produced by thr Marine-Oberbaurat at Kiel in 1918. Plans of the beast.

The other prospect for a “U-Kreuzer” or underwater cruiser, was to just hunt down con,voys to the mid-Atlantic and beyond, at the fringes of US coastal and territorial waters. It was far more difficult to guard these areas, since the US were still neutral and in fact rather a business partrner provided a ship could get there in the first place. Indeed the British imposed a strict naval blockade and very few blockade runners made it through. Hence the idea of a cargo submarine, that could evade these patrols by just submerging.

Sure, the amount of cargo was to be limited to a few hundred tonnes, but it was calculated that simply carrying the most valuable goods needed in the US (like some rare chemical and phamarceutical products) and in return, even more badly needed in Germany (like rubber and some metals) was worth the industrial risk and financing. Backed by the largest Banks in Germany, and three large “cargo U-Boote” were ordered for the Deutsche Ozean-Reederei (DOR). SS Deustchland, Bremen and Oldenburg. SS deustchland was completed in June 1916 and undertook the first of two trips that were extremely profitable and largely covered the construction expanses for the three boats.

SS Bremen disappeared in her first trip (likely sunk by the RN) and SS Oldenburg was never completed as a cargo sub, and instead requisitioned by the German Navy for conversion as military sub. That was also the fate of Deustchland that became U 155 in 1917. In total, six were in service, but their military conversion led to many compromises. Their initial shipyard, Flensburger Schiffbau-Gesellschaft shipyard that created essentially the pressure hull, separated from the outer hull to keep some secret, was contacted, as well as Reiherstieg, Hamburg that made all follow-up boats, and of course Friedrich Krupp Germaniawerft shipyard in Kiel that completed all these boats, as far as March 1916, when the first boat was launched.

By creating Project 46, the German naval staff wanted Germanawerft to design a military version of the SS deustchland. The latter was indeed more suited to carry cargo than to do combat, with her very wide beam, short hull and very deep draught, low speed, and two large holds. So the first task of the Marine-Oberrat (Design Bureau) of Kiel, working with Germaniawerft, was to create a mich faster submarines. Compromises in construction led also to the fitting of just two torpedo tubes forward on the U 151 class, so the Navy wanted to have the same standard six as its current oceanic models like its Ms types, six tubes, four forward, two aft.

Project 46 was to be so well armed for surface actions, with a combination of two 15 cm cruiser guns and two 8.8 cm light guns they were also called “artillerie-boote”. That combo was adopted due to the fact captains estimated surface raiding was far more efficient with that type of artillery to quickly dispatch any civilian vessel in spots not covered by British escorts. Indeed the range of British flower class sloops at the time was 2,000 nmi (3,700 km) at 15 kn (28 km/h) that did the bulk of the escort work across the Atlantic left a gap between the mid-Atlantic and US territorial waters that could be exploited. The USN at the time by late 1916 took no part in escort work, and before the US entered the war in April 1917, this was “open range” for the new “U-Kreuzer”.

Design work for Project 46 was ready in July 1916 a month after SS deustchland was completed and ready for departure. The naval staff obtained to have these “cruisers” protected by armour plating, for the conning tower and ammunition trunking. The armament location and ammunition feed were standardized with the U 151 class, in fact their construction and the conversion of the first two and follow-up U 151 class boats. The first three boats were ordered at Germaniawerft as hull n°300-302 in August 1916. Construction was ongoing when by February 1917 SS Deustchland was requisitioned, followed by SS Oldenburg still in construction for conversion, so their own armament setup went into parallel.

Despite having earlier number, U-139 to U-141, the three Project 46 Boats were completed well after the conversion of the U-151 class boats, and actually U-140 was commissioned first in March 1918, U 139 second in May and U 141 third in June 1918 so they had only few patrols to their credit. This did not prevented the naval staff to launch the improved Project 46A in 1917, many being launched by none ever completed at V-Day. Retrospectively, the “U-Kreuzer” concept had little effect to the course of the war, as they came out too late to make a difference, but they would have immense repercussions and influence on submersible design in the interwar, just as the Type XXI of World War two had an immense influence in cold war submarine design.

Design of the class

Hull and general design

Internal Layout of the U 139 class

The U 139 class were significantly larger than the U 151 class because they were essentially stretched out, for the same beam. They reached 1,930 t (1,900 long tons) surfaced and 2,483 t (2,444 long tons) submerged, making them the largest submersibles ever built at the time. They were much longer than the U 151 at 92 meters (301 ft 10 in) overall versus 65 meters (213 ft 3 in) -almost 100 ft longer- to create a better hull ratio, and hence gaining extra surface speed, well helped by their new bow design, very angular and making a long curvy connection to the keel. It was shaped like a knife.

That extra lenght enabled much finer entry lines. The pressure hull was also longer at 71.50 m (234 ft 7 in). The outer beam reached 9.12 m (29 ft 11 in) overall, so they were even beamier than the U 151 (8.9 metersor 29 ft) for a pressure hull of 5.75 m (18 ft 10 in). The draught was slightly reduced, from 5.30 to 5.27 m (17 ft 3 in). Total height from the keel to the top of the CT was now 11.20 m (36 ft 9 in).

The general outlook thus differed considerably from the U 151, with much finer hull lines forward and aft, a deck that was substantially enlarged as a support for the artillery, with the main 15cm placed slighly offset off-axis port and starboard either side of the CT, for better fire arcs. The two 8,8 cm guns were in an inner perimeter closer to the CT, in echelon outwards of the main guns. They were semi-high angle for limited AA defence as well. Cargo holds has been eliminated but the U-139 still had a prize crew hold for 21 men forward, close to the crew’s quarters.

The forward torpedo room was much larger and integrated this time directly the spare torpedoes (24 total) for closer reload, but there were still large hatched above for upper reload. The high draught enabled a full two-deck configuration, with men able to stand in the lower level that inregrated the batteries like all previous designs amidships, in two groups, but many former posts were now located below as well. Ammunition magazines were huged and located deep down for protection. The conning tower was surrounded by a wing-shaped fairwater topped with a deck, on which was installed the forward usual helmsman’s post and his wheel, generally covered with canvas, and the main bulwark for the officers’s watch deck behind, integrating a wave breaker and navigation lights.

The hull had the usual net-cutting saw forward, a protective cable running fore and aft and anchored on top of the CT. The latter, on its aft platform, mounted a small rangefinder for artillery work. There were two periscopes in the CT, one for watch and one for attack. The hull has the usual anti-collision bars fore (protecting the fixed forward diving planes) and aft (protecting the aft diving planes) whereas the propellers were protected by bars ending with an outer axle for these aft diving planes. There were two telescopic radio masts folded down along the port side ballast bulges.

Powerplant

U 139 interned in Cherbourg, NARA

The main engine room was located aft, under the “X” 15cm mount, on two decks to accomodate enormous diesels tailored for this class. The main electric motors were located in the next engine room, separated by a flat bulkhead, with upper hatch access. Itself had a bulkhead and upper hatch separating it from the aft torpedo room. There was enough room to fit an auxiliary engine room aft of the CT and main contl room at the lower level. The two MAN diesel engines 6-cylinder, 4 valve, 1.500 PS each or 3,300 PS (2,400 kW; 3,300 shp) total surfaced and the usual pair of SSW (Siemens) electric engines rated for 890 PS each (880 hp) each or 1,780 PS (1,310 kW; 1,760 shp) total submerged. This made for a top speed, surfaced, of 15.8 knots (29.3 km/h; 18.2 mph) surfaced thanks to their 2.10 m (6 ft 11 in) propellers and 7.6 knots (14.1 km/h; 8.7 mph) submerged.

At the end of the day, these however had a range comparable to the former Deustchland/U 151 class, likely c280 tonnes of oil after modifications, still comfortablle enough for 17,750 nautical miles (32,870 km; 20,430 mi) at 8 knots (15 km/h; 9.2 mph) surfaced, and thanks to larger battery power, 53 nautical miles (98 km; 61 mi) at 4.5 knots (8.3 km/h; 5.2 mph) submerged. For liaison to the shore, these boats also carried the usual cutter, protected under a hatch below the outer hull deck.

Protection

Unlike previous boats, the U-139 class had a thicker pressure hull made of 25 mm (0.98 in) plating. The hull was divided into seven main compartments by six flat bulkheads of that same thickness. To avoid flooding in two-deck tall compartments aft, the hatch was located quite high and accessible by a ladder. The slightly thicker outer hull enabled a diving test depth of 75 m (246 ft), more than the usual 50m of Ms boats. Crush depth was estimated twice as much. What’s new and unique about the design, is the amount of armour protection that was introduced: The conning tower’s command centre was protected by 30 to 90 mm (3.5 in) of plating (the walls were cast steel), and the ammunition trunking by 25 mm or 1-inch.

Armament

The U 139 and U 151 were armed the same way, with two cruiser guns, 15 cm (5.9 in) SK L/45 deck guns with 980 rounds, stored below and accessible through deck hatches, and two 8.8 cm (3.5 in) SK L/30 deck guns with 200 rounds placed as seen above. The torpedo count was larger with four at the bow, two in the stern and 24 torpedoes in reserve. Thanks to their high speed, this allowed them to engage even armed merchant vessels, left to protect the convoys far out at sea unlike sloops and destroyers.

14.9cm/37 SK L/40 C/97

If installed, these 1908 guns were protected by bulwarks for and aft. These 15 cm SK L/45 were classic light cruiser guns also used as secondaries on many ships, from armoured cruisers to battleships and battlecruisers, made for both casemates and turrets. They were constructed of an A tube and two layers of hoops, a Krupp horizontal sliding-wedge breech block.

Specs

Mass: 5,730 kgs (12,630 lb) for 6.71 m (22 ft), barrel 6.32 m (20 ft 9 in)L/45.
Shell: Separate loading quick fire 149.1 mm (5.87 in) diameter.
Breech: horizontal sliding-wedge, Hydro-spring recoil
Elevation 20°, 5-7 rpm, MV 840 mps (2,800 ft/s), range c14 km.

8.8 cm Schnelladekanone Länge 30 naval deck gun

The 8.8/27 TK L/30 C/08 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. When combined with the heavy 15 cm guns, they were located in echelon either side of the conning tower with 764 rounds each. Four deck gun was an unprecedented number for a submarine, really making true their “cruiser submarine” concept.

8.8cm specs

Weight: 644 kgs (1,420 lb) oa 2.64 m (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°.

Torpedo Tubes

Either they carried six tubes in pairs over the deck (Deustchland only) whereas Oldenburg aka U 155 and U 151 had two classic bow tubes. But all had the same 50cm tubes made for the standard 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. The first two boats had 24 in store, the latter 18. The way the torpedo system worked on U-155 (former Deustchland) is somewhat foggy. It seemes these were traversing banks which inspired the French postwar. In any cases, they had to be reloaded when surfaced, making this impractical. Later in 1918, they were removed and she had the same two bow tubes as her sisters.

50cm G7 torpedo specs

Specs: Weight: 3,009 lbs. (1,365 kg), Overall Length: 276 in (7,020 m).
Explosive Charge: 430 lbs. (195 kg) Hexanide 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. Note that some sources states these were G6 torpedoes,

Profile awaited

⚙ specifications
Displacement	1,930 t surfaced, 2,483 t submerged
Dimensions	92 x 9.12 x 5.27m (301 ft 10 in x 29 ft 11 in x 17 ft 3 in)
Propulsion	2 shafts diesels 3,300 shp surfaced, 2 EM 1,760 shp submerged
Speed	15.8 kts surfaced, 7.6 knots submerged
Range	17,750 nm/8 knots surfaced, 53 nm/4.5 knots submerged
Armament	6× 50 cm (TTs (4 bow, 2 stern, 24), 2× 15 cm SK L/45, 2× 8.8 cm SK L/30
Test depth	75 m (246 ft)
Crew	6 officers, 56 ratings (1+20 prize crew)

Career of The U-139 class

U-139 in Cherbourg 6 February 1919, NARA, USN archives.

The Type 139 submarines were created for long-range missions, able to go south across the Equator, west across the Atlantic, and operating independently. A network of supply vessels in distant stations were planned. These were the costliest submarines ever built in germany at 8.7 million Marks at the time, with the 15 cm guns accounting for around 7% of the cost.
The choie of skipper for such a grounbreaking “secret weapon” was paramount, so no less than Lothar von Arnauld de la Perière, U-Boat ace of aces of all times, commanded U-139, first in class. Hwever that late in the war he only managed to single four ships from May 1918, and the last ship in World War I, on 14 October 1918 (NRP Augusto de Castilho, Portuguese armed mine hunting ship).

They were named after successful wartime U-Boat commanders did in action, U-139 as SM. Kapitänleutnant Schwieger (after Walther Schwieger, who had sunk RMS Lusitania in 1915.) and U-140 s SM. Kapitänleutnant Kophamel. U 141 remained unnamed. After the Project 46A were ordered, an even larger U-cruiser was planned, Project 47, which never reached construction. Displacement was 2,500 tons, expected top speed 21 knots (39 km/h; 24 mph), armed with four 150 mm guns, six torpedo tubes, two firing to the side. The U 139 class had been fitted with prize crew holds in 1916, but they ended used in unrestricted warfare, so it was seldom use in reality.

SM U 139 (Kapitänleutnant Schwieger)

U-139 was ordered on 1 August 1916 at Germaniawerft, Kiel, Yard number 300. Laying date unknown, likely late 1916 up to January 1917. She was launched on 3 December 1917 but completed second and commissioned on 18 May 1918 (her sister U 140 was commissioned earlier). She was given the name of Walther Schwieger in the commissioning ceremony, attended by the naval staff and Kaiser.

She entered the “U-Kreuzer flotilla” already also counting the converted U-151 class boats, so some experience with their handling could be passed onto training the new boats. Under the command of ace submariner Lothar von Arnauld de la Perière, she only made a single war patrol, starting in september, but she trained all May to August 1918, just as the Germans were launching the spring offensive on the western front. In this September-October patrol she sunk four ships for 6,788 tons, far less than U 155 (ex-Deustchland) for example despite all the promises. It was just too late.

On 1st October 1918 she sank the British cargo ship Bylands (3,309 GRT), and the same day also bagged the Italian SS Manin (2,691 GRT) and damaged their accompanying escort, the armed merchant cruiser HMS Perth (2,502 t) or “armed boarding steamer” for the Royal Navy, usually deployed for blockade purposes, before submerging and getting away unscaved. The following day she sank a small coaster, the portuguese Rio Cavado (301t). But prizes were rare. On 14 October 1918 she sank the Portuguese Navy ship the Augusto De Castilho (487t).

This action was peculiar, as she attacked a small convoy made of the Portuguese civilian steamer SS São Miguel, escorted by the Portuguese Navy small naval trawler NRP Augusto de Castilho in the Atlantic. Augusto Castilho, an armed tall ship, covered the escape of São Miguel, and engaged the surfaced U-139 for an amazing gun duel lasting for hours, until she was destroyed. Her crew was posthumously awarded back in Portugal where this rare action of WW1 for the Portuguese Navy, at war with Germany after many incidents by August 1916. That was the last gun battle ever between a tall ship and a German U-Boat, which were already a rare occurence, and the last armed tall ship ever sunk.

U-139 came back in November and wa sinactivated, pending surrender provisions. She was awarded to France on 24 November and shortly afterwards arrived at Cherbourg to be recommissioned as “Halbronn” and used extensively until 24 July 1935, sold and broken up.

SM U 140 (Kapitänleutnant Kophamel)

U-141 was Ordered on 1 August 1916 from Germaniawerft, Kiel, Yard number 302 but only launched on 9 January 1918. She joined the U-Kreuzer flotilla after completion at an unknown date, trained until she was declared ready in April, albeit it seems this was still training and started her only combat patrol as reported before her sister U 193 under command of Kophamel, in July-August, sinking according to uboat.net 7 ships for 30,594 tons making her the most successful in class.

On 27 July she arrived on the east coast of the US and sank the cagro ship SS Porto (1,079 GRT) and on 2 August the Japanese large cargo Tokuyama Maru (7,029 GRT), then two days later on 4 August 1918 she sank the large US tanker O. B. Jennings 10,289 GRT in the Atlantic, 100 nautical miles (190 km) off the coast of Virginia. She rescued one sailor, that became POW. The following day, still reoaming alon the US east coast, she sank the cargo ship Stanley M. Seaman (1,060 GRT) and on 6 August the Lighthouse Service steamer Diamond Shoals LV71 (590t) and later that day the cargo ship Merak (3,024 GRT). The cargo ship was shelled at Diamond Shoals or wrecked on Diamond Shoals while trying to avoid the attack.

Her last victim of the war was on 21 August 1918 the British Diomed, 195 nautical miles (361 km) east south east of Nantucket, with the loss of two crew. U 140 was surrendered to the allies on 26 November 1918. Attributed as war reparation to the United States, she was carefully studied and used for testing as USS U 140 until stricken, scuttled by gunfire, by the destroyer USS Dickerson (DD-157) as target in the Atlantic, off Cape Charles, Virginia, on 22 July 1921.

SM U 141

U-141 had been ordered on 1 August 1916 from Germaniawerft, Kiel, laid down likely in March-April 1917 at Yard number 302, launched on 9 January 1918 and commissioned on 24 June 1918. She started “operations” under Kptlt. Constantin Kolbe on 24 June, but was still training before she could makde a single war patrol, for whatever reason. So she sank no vessel. On 26 November 1918 she was surrendered and awarded as war reparation to Britain. She was carefully studied, and used as target on 7 October 1920 but not sank. She was instead stripped off, towed and broken up at Upnor in 1923.

The U 139 in Foreign Use

U139 moored in Brest, 1919, waiting for standardization and recommissioning as Halbronn in French service.

As seen above, all three U 139 class, as the only ones effectively completed and commissoned in WWI were superb examples of what a cruiser submarine can be. They were even more interesting than the converted U 151 class, too limited by their initial cargo submarine features to really stand up as proper military boats, albeit they collectively sank close to 300,000 tonnes, far more than the U-139’s 37,382 tonnes. U 155 alone sank 121,328 GRT. But Project 46 boats were the first properly combat cruiser submarines ever designed. And by many aspects, likely the best U-Boats by sheer range, speed and artillery any nation possessed at the time. They would also remain the most heavily gun-armed submarines before several nations decided to explore the concept in turn.

All three were indeed awarded in 1918 to the entente powers, eager to have their hands on these superb toys; France (which of the three used U 139, renamed Halbronn the most until 1935), the US, with U 140 (short service as USS U 140 for tests and trials) land U 141 in RN test units (no formal commissioning) in 1919-1922. From there, the French designed the even more impressive Surcouf, and pushed the boundaries of what a submarine cruiser can be, replacing the 15 cm deck guns by 20 cm guns in a turret, a proper fire control and aviation spotter to boot.

Halbronn (ex-U139) and Gustave Zédé, Brest, February 1919. Photo by Machinist John G. Krieger (thus US archives)

The Americans worked on their “V” series in the immediate postwar yards, and if their initial 1919-20 humongus cruiser submarine projects (they would have dwarved any submarine ever built, past of present) were never realized, they still made the very large USS Argonaut and the Narhwal class, their only three “proper” cruiser submarines, which ended used for special operations in WW2 instead of as commerce raiders. By the way one of the graal looked after was to achieve a fleet speed (21) fleet submarine, parlty inspired by the German Project 46A and Project 47.

The Royal Navy was also interested by the concept, albeit their own general doctrine of world’s supreme fleet in being did not included submarine raiding on trade lines, as it already possessed the most of these, and largest trade tonnage by far of any nation. Still, the type could be useful, and apart the very large M-class and K-class, the RN only commissioned postwar the HMS X1 but the latter was quickly decommissioned after being plagued by engine issues, a bit like the US, the large diesel powerplant and diesel-electric combo was difficult to achieve. Britain never returned to such concept, neither the Germans themselves, which stuck to the large ocanic standards Type IX in WW2. However the concept of U-Kreuzer proved also highy influencial in Japan, which started their Kaidai serie based on ex-German subs, and Italy, with concepts such as the Fieramosca and Micca.