Design, Manufacture and Detail
(with permission of Dave Krakow, www.prinzeugen.com)
The technical history of the S-Boat is a tribute to the imagination, determination and resourcefulness of German engineers. Although the treaty of Versailles was meant to prevent Germany from taking up arms in a war of aggression, its practical effect was to stimulate an ingenious and modernistic arms development program. Turning obstacles into advantages, German engineers designed weapons which both outwitted the restrictions of the Versailles treaty and capitalized on new technologies and tactics that could enable a small, lightly equipped nation to defeat a more powerful but anachronistic enemy. The rapid defeat of France in 1940, despite its overwhelming numerical superiority over Germany in weapons and troops, was total vindication of this program. The S-Boat is a classic example of Germany’s Versailles-influenced weapons engineering. Focusing on a boat considered too insignificant by the Allies to be regulated by the treaty, the Germans created a scaled down warship well-suited for naval Blitzkrieg. Heavily armed and fast, it could inflict great damage on a larger enemy and escape unharmed. Its sturdy design showed great foresight into its future operational role and emphasised high quality over mass production. From very the beginning of the torpedo boat program, German Naval Command required boats suited for combat in North Sea conditions. A series of trials with a broad variety of designs began in 1920 under cover of developing a fast “submarine chaser,” Most initial programs concentrated on short planing hulls commonly used for speedboats. This surface skimming design is ideal for fast boats in calm waters but loses its chief advantage of efficiency when waves slam the flat hull bottom. Furthermore, weight is a critical issue, and the iridescent plume of water created by a planing boat moving at high speed is visible over great distances at night.
In 1928, in light of these limitations and the dismal North Sea weather, Naval command elected to concentrate strictly on a round bottomed displacement hull. Their attention was drawn to Oheka II , a highly innovative luxury motor yacht built in 1927 by the German boatyard Luerssen for a Jewish banking tycoon who emigrated to the United States from Germany. The name “Oheka” originated from a monogram of its owner’s name, Otto Hermann Kahn. It’s round bottomed hull was 22.5 m long, and displaced 22.5 tons. It reached a top speed of 34 knots, making it the world’s fastest boat in its class. There is no basis in fact for the common misconception that Oheka II was a “rum runner” used for smuggling.
In Oheka II, Luerssen overcame many of the drawbacks of the round bottomed displacement hull. The boat ploughed through the water by the brute force of three 550hp Maybach engines. The composite use of wood planks over alloy frames reduced weight. The inefficient tendency for round hulls to “squat” stern-down in the water at high speeds was counterbalanced by a hull form that flattened towards the stern, providing hydrodynamic lift where it was needed. Oheka II’s combination of speed, strength and seaworthiness was exactly what Naval command wanted. In November 1929, Luerssen was given a contract to build a boat to the same basic design, but with two torpedo tubes on the forecastle, and a slightly improved top speed. It was to become S-1, the Kriegsmarine’s first Schnellboot and the basis for the all other S-Boats built during World War 2. Experimentation with S-1 and the intial batch of five additional boats led to immediate improvements and innovations. For example, beginning with S-7 (1933) the increased reserve buoyancy of a knuckle added at the bow prevented the boat from nosing into waves in foul weather. Another key innovation was the addition of a special rudder arrangement beginning with S-2 (1932). Port and starboard of the main rudder were two smaller rudders which could be angled outboard to 30 degrees. Known as the “Luerssen Effekt,” at high speed, the angled rudders drew a ventilation air pocket slightly behind the three propellers, increasing their efficiency, reducing the stern wave and keeping the boat at a nearly horizontal attitude. A wedge was added to the lower stern beginning with S-18 (1938). This deflected the water flow slightly downwards, counteracting any tendency for the hull to settle into the water as speed increased.
Improvements were made to the boat’s superstructure. On early boats, the commander stood outside on the deck behind a spray shield. Behind him in the wheelhouse stood the helmsman, navigator, radio operator and engine telegraphist. The commander communicated his orders through flexible voice tubes, or via a seaman equipped with an headset intercom. The S-26 class (1940) instituted a 34.9m hull and several design changes. The torpedo tubes were enclosed in a decked-over forecastle, increasing interior space and reserve buoyancy. A cockpit was set into the wheelhouse roof, placing the commander in a centralized position with better visibility and shelter. From there, he could speak through portholes directly to the wheelhouse forward and navigator aft. His “instrument panel” consisted of glass windows through which he could observe a compass and the wheelhouse interior. (Note that there was no steering wheel in the cockpit.) Starting with S-30 (1939) several boats were built with a slightly smaller hull, 32.7m, and with the old style wheelhouse. The S-38 class was a continuation of the S-26 class with simplified ventilators and other minor changes. Experimentation with S-67 (1942) led to a design for a partially armour plated cupola, the so-called Kalotte (skull cap), over the bridge. The added armour was a countermeasure to the growing firepower of British escort craft encountered in the English channel. This led to an armored bridge variant of the S-38 class, the S-38b which was delivered from the boatyards with the armor already in place.
Shortly thereafter, the S-100 class (1943) was designed from the start to incorporate the Kalotte and additional armament including a twin 2cm amidships and a 3.7cm gun aft. The S-100 design also eliminated a number of unnecessary details such as skylights over the engine rooms. A final variation Schnellboot, the type 700, was designed with extra defences against pursuing Allied craft. It was to carry two stern firing torpedo tubes in addition to the usual bow tubes, plus a special 3cm gun in the bow turret. Due to its weight, it required a powerful MB518 motor. However, production of the MB518 was cancelled due to Allied bombing, and the S-700 was never built; S-701 to S-709 were completed as S-100 class boats. This is confirmed by the photographic evidence. There were many minor wartime changes to the armament, superstructure, and hull dimensions, but the hull design remained basically unchanged from S-18 onwards. In late July and early August 1945, future president John F. Kennedy visited defeated Germany with US Navy Secretary James Forrestal. As a former PT boat captain, he was naturally interested in the German counterpart so he made a point of carefully inspecting an intact “E-Boat” at Bremen. Kennedy’s diary records his conclusion: the Schnellboot was “far superior to our PT boat.”
