It was fortunate for the Allies that Germany was unable to get I her Type XXVI submarine into production before she was defeated in World War II. What was the Type XXVI subma-rine? It was Germany’s attempt to beat the Allied convoy system by means of a very fast convoy-killer submarine. Had she succeeded, the employment of this new weapon system would have been as important to the German war effort at sea as the development of panzer tactics was to German land warfare.
Although German scientists had been working to develop nuclear power, they were not very far along. In a separate effort Professor Walter and his engineers pursued a two pronged approach to give German submarines the high submerged speed of about 25 knots with good endurance. They sought to accomplish this by designing a streamlined hull and powering it with powerful gas turbine(s) using concentrated hydrogen peroxide (H20~ and fuel as the energy source. [Ed. Note: See Dick Bloomquist’s article AlP- A Historical Permective in the July 1993 Submarine Review.) This system became known as the Walter propulsion system, and with it the streamlined Type XXVI submarine could have evolved as the German weapon system to counter Allied convoys.
Convoys and Wolfpacks
To reduce Allied losses to German submarines in World War II, most of the shipping in the North Atlantic was organized into large escorted convoys. Convoys consisting of as many as 50, 60, and even 100 ships were not uncommon. As a result, when a single German submarine detected a convoy it had limited ability to inflict damage because of its limited supply of torpedoes, low submerged speed and endurance, and counter attacks by convoy escorts.
To bring more torpedoes into an attack, Admiral Doenitz established the wolfpack system. Under this system, a submarine making contact on a convoy reported the contact to the submarine command headquarters by radio. The contact maker then continued to shadow the convoy until the headquarters could direct additional submarines to the scene. Although the wolfpack system was fairly effective, the convoy system allowed large quantities of men and war supplies to safely cross the Atlantic. In any event, the attack tactics employed by German submarines remained essentially the same-individual submarine attacks on individual ships.
Search for a Better Convoy Attack System
Recognizing the need to attack convoys more effectively, a few German submarine tacticians and scientists sought means to sink more convoyed ships. Among these were Professor Walter, a man with a keen grasp of those fundamentals of physics, chemistry and engineering needed to improve German submarine capabilities. Working with submarine design groups and building yards, Dr. Walter set out to design an attack submarine able to run sub-merged at high speeds for many hours without intake of atmo-spheric air. The culmination of that effort almost brought the Type XXVI submarine into production by the end of the war, although apparently none became operational. While the develop-ment of these submarines was in process, submarine headquarters personnel set out to design tactics for attacking convoys with Type XXVI submarines .
Development of the Type XXVI Submarine
The Walter Propulsion System. As noted above, the basic concept for this system used stored concentrated hydrogen peroxide (H702)-called Ingolene-to replace air as an oxidant for creating energy to drive a gas turbine. The turbine was coupled to a propeller shaft through a reduction gear. In many respects the Walter system was limited to several hours at high speed due to limited storage capacity for hydrogen peroxide. Nonetheless, this performance was outstanding compared to that of the conventional diesel/battery powered Type VII and IX submarines then in operational use. Those types had a maximum submerged speed of only 7 knots at their one-hour battery discharge rates.
Walter system submarines were also equipped with moderate sized diesel engines for running on the surface and snorkeling, and electric storage batteries for low speed submerged running.
By war’s end the development of the Type XXVI submarine had progressed in steps almost to the point of operational capability. Y.80 The first high speed submersible powered by the Walter system was an experimental propulsion test model designated the V .80. She was small-an 87 ton submarine driven by a 2,000 horsepower turbine. It attained a submerged speed of 2S knots. Professor Walter reported that he had personally operated the controls during trials and found that steering and depth control presented no problem at top speed.
Type XVII. The next development step was a streamlined experimental prototype of an operational design with two bow torpedo tubes. Four of these were built. They were small, displacing about 260 tons. Fitted with two 2,SOO horsepower turbines coupled to a single propeller shaft, their maximum submerged speed was 26 knots. Hydrogen peroxide was stored in plastic bags set into tanks on the sides of the hull. A 210 h.p. diesel was provided for surface/snorkel running.
Type XVIIB. The next step was planned as the operational version of the Type XVII. Six were built or under construction at war’s end. Their length was about 136 feet, beam about 11 feet, and draft 14 feet. They were larger than the Type XVII with a submerged displacement of about 340 tons. Although designed for two Walter system 2,SOO h.p. turbines, they were fitted with only one because of shortages. Powered by the one turbine they had a maximum submerged speed of about 21 knots. Maximum speed with two turbines was calculated to be 2S knots, and endurance at that speed was expected to be five hours, and range about 12S miles. Endurance at IS knots was greater, about 11 hours, to provide a range of 165 miles.
Like the Type XVII, the Type XVIIB was fitted with two bow torpedo tubes and had a total capacity of four torpedoes. Test depth was about 400 feet. The complement was 3 officers and 16 enlisted men.
Tyne XVIII. The Type XVIII was planned to be the largest version of the Walter system propelled streamlined submarines. It was designed for a submerged displacement of about 1,800 tons and a maximum submerged speed of 27 knots. At lower speeds it was to have an endurance of about 7 hours at 24 knots, and 22 hours at IS knots for corresponding ranges of 17S and 330 miles respectively. The program was terminated due to wartime need for more immediate production of operational submarines. However, the streamlined hull design was incorporated into the mnre conventional diesel/battery Type XXI submarine.
Type XXVI. This was the last step in the wartime development program of a German high speed, long endurance submarine. Two were under construction at war’s end, one of which was scheduled to be completed during the summer of 1945.
Type XXVI was a relatively large streamlined submarine of about 1,000 tons with an initial design length of approximately 185 feet, beam of 12 feet and draft of 19 feet. It is understood that these values were later increased. She was equipped with the Walter propulsion system featuring a single 7500 h.p. turbine to drive a single shaft. The system was designed to provide a submerged endurance of about 15 hours at 15 knots for a range of 225 miles, or about 6 hours at 24 knots for a range of about 125 to 150 miles. She had a relatively small battery for low speed submerged operations, and one main 580 h.p. diesel, plus one 265 h.p. auxiliary diesel, for surface/snorkel cruising. Test depth was 450 feet. Crew size was 4 officers and 26 enlisted men.
A unique feature of the design was the arrangement of its 10 torpedo tubes. Four were conventionally mounted in the bow, and three on each side were pointed aft and outboard at an angle of about 9°. The orientation of the side tubes permitted a torpedo to be reliably launched at speeds up to 15 knots, whereas launching from the bow tubes was limited to speeds of less than 6 knots. Torpedo capacity was 10; i.e., one in each tube, with no reload capacity.
A Hypothetical Type XXVI Wolfpack Attack
In early June 1944 Allied troops landed in Normandy to begin the Great Invasion of the continent. Earlier in 1944, 90 Allied merchant ships had been assembled on the U.S. East Coast to form the large convoy, US/UK-45. Its mission was to deliver war materials and personnel to England in preparation for the coming invasion. The convoy was intercepted by the German Type XXVI submarine, U-3606 shortly after noon on a typical North Atlantic overcast and stormy day. The convoy was then over two-thirds of the way across the Atlantic.
The Convoy. The convoy was steaming in rectangular formation. The front consisted of nine column-guides deployed 700 yards apart on a line-of-bearing from the formation guide. The column-guides were on parallel courses with nine ships following in the wake of each at 600 yard intervals. The width of the convoy was somewhat greater than three miles and the length somewhat less. Plowing into heavy seas built up by strong winds from the northeast the convoy advanced toward England at 8 knots. Destroyers and destroyer escorts assigned to protect the convoy against submarine attack normally patrolled outside the perimeter of the convoy but on occasion darted between columns to keep the convoyed ships in a semblance of order. While so engaged the escorts were unable to devote full time to their anti-submarine duties.
Intercept and Attack. U-3606 was one element of a submarine wolfpack of six Type XXVJ’s deployed on a north-south scouting line 100 miles long which crossed expected convoy routes. In accordance with established procedure U-3606 reported the convoy’s position, course and speed to the Submarine Command Headquarters upon making contact. She also reported that she was changing position from the convoy’s south flank to its north flank to gain better position for reasons of both visibility and attack position. U-3606 crossed under the convoy at 15 knots and emerged a half hour later in position to both observe and attack. Within three hours four of U-3606’s consorts which had proceeded a high submerged speeds were able to rendezvous with her on the north flank of the convoy. The fifth Type XXVI was too distant to reach the attack station during daylight hours.
Following standard wotfpack procedures, U-3606 as contact maker, took over as Officer in Tactical Command and issued instructions to wolfpack submarines. He ordered them to take stations 600 yards apart in column on a line paralleling the northern flank of the convoy. At 3:15 each of the five attacking subs turned in a time-coordinated submerged maneuver to approach the convoy’s flank and loosed 20 torpedoes from their bow tubes into the mass of the convoy. Each then made a 1800 turn to the left in the direction the convoy was heading and within minutes loosed another 30 torpedoes at the convoy from their side tubes. Explosions followed by smoke and fire which illuminated the area created a scene of utter confusion. U-3606 remained in the area to gather further evidence of damage inflicted on the convoy while the other four attackers sped away submerged at 15 knots to clear the area and then headed for their base. U-3609, the fifth Type XXVI, arrived at the attack scene three hours later with a full load of 10 torpedoes and set about finishing off the damaged ships. The tally for the initial attack was 40 hits out of the 50 torpedoes fired, plus seven damaged stragglers sunk by U-3609. None of the U-boats were attacked or damaged. Total ships sunk was later evaluated as 30 sunk out of the original 90 in the convoy, or a loss of one-third of the convoy in a single Type XXVI wolfpack attack.
Attack Tactics. Special tactics for Type XXVI wolfpack attacks on convoys had been developed by tacticians of Submarine Command Headquarters. Their solution was based on the applica-tion of simple probability theory to the problem. This is illustrat-ed in Figures 1 and 2 which depict the path of a single torpedo fired on a straight course into the 90 ship convoy described above. Figure 1 shows the probability of hit of a single torpedo fired without aim at a single column of ships 450 feet (150 yards) long, steaming 600 yards apart in column. The probability that the torpedo will hit one of the ships is 150/600 or 25 percent. Conversely, the probability that the torpedo will miss hitting a ship is 450/600 or 75 percent.
View full article for table data
In the case of a large convoy (Figure 2) the torpedo that missed a ship in the first column will continue on its path to hit or miss a ship in the second column. The probability that the torpedo that missed a ship in the first column wilI also miss a ship in the second column is 0.75 x 0.75 or (0.75)2 = 56.25 percent. In like manner, the probability that the torpedo will miss ships in all nine columns is (0. 75)9 or about 7.5 percent, and the probability that this torpedo will hit at least one ship in the convoy is 1-7.5 per cent or about 92.5 percent. To summarize, the probability, Pk, that a single torpedo will hit a ship in a multi column convoy is:
View full article for table data
An advantage of this tactic is the simplicity of a fire control system which produces excellent results. The probability of hit is independent of: (1) convoy speed and precise course, (2) the distance between columns provided that the torpedo has sufficient range to cross through all columns, and (3) the angle at which the torpedo crosses the convoy course. To this end, a 30 knot torpedo with range capability of about 10,000 yards is a very satisfactory weapon. Further, no torpedo homing device is required to achieve high probability of hit.
Conclusions
- Simple torpedoes and simple fire control systems can wreak havoc with large convoys if large numbers of torpedoes are fired into the mass of the convoy.
- Although the convoy system was effective against conven-tional diesel-electric submarines in wwn, it would not have been effective against attacks by Type XXVI submarine wolfpacks.
- The tactics described above are also effective against largeformations of combatant and support group ships.
[Ed. Note: Mr. Gruner qualified in submarines in 1936. He made ten war patrols. He served as Executive Officer of PIKE, SUN-FISH and APOGON and commanded SKATE (SS 305) for three patrols. After the war he worked for Lockheed and did the development plan for the Polaris missile. He is a member of the League and a frequent contributor to the Review.]
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