The Explosive Boats of the Kriegsmarine

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The three-man command boat was equipped with an ultra shortwave transmitter (7-metre band, manufacturer Blaupunkt).

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Besides one-man torpedoes and midget submersibles, K-Verband Command also operated Sprengboote, or explosive boats. The historical predecessors of these so-named Linsen (the word in German means ‘lens’ or ‘lentil’) were the fireships, small sailing vessels loaded with easily ignited substances (tar, pitch, cotton waste, oakum or oil) which were sailed or rowed towards the target vessel. In proximity to the latter the cargo was set ablaze and the fireship made fast to the victim by hooks or chains. Fireships were used at the siege of Syracuse in 413 BC and even in the early 19th century formed part of the regular inventory of the various battle fleets.

In 1909 the German Imperial Navy awarded the Lürssen Werft a contract to build a 9-metre long experimental explosive boat Racker (villain) with a top speed of 27 knots which would be controlled using two 50-metre long wires run from a spool.

The second experimental boat, the 11-metre long Havel, also developed by Lurssen for remote control and equipped with 100 hp engines, achieved a speed of 33 knots at Schwerin in 1911. The trials headed by Kptlt Ehrhardt were not considered satisfactory.

After the outbreak of World War I the German Navy revived the programme and in 1915/1916 seventeen remote-controlled boats (FL1 to FL17) were constructed. Most of them saw action on the Flanders coast. They carried a 700 kg charge and were operated by means of a 16-mile long (later 27-mile long) cable from a land station. Even after the introduction of radio, however, remote control proved unreliable and was not a suitable alternative to having personnel available to make decisions on the spot.

In the Second World War it was not the Kriegsmarine but experts of Brandenburg Regiment zbV 800, a special unit of the German Abwehr, which took up the concept. On 27 September 1939 Dr Theodor von Hippel, then Hauptmann on the Staff of Abwehr/Ausland II, obtained approval to form a company of experienced men for the impending campaign in the West, and on 15 October Admiral Canaris, Abwehr head, told him to proceed. The task of this special unit was to be commando operations behind enemy lines often wearing enemy uniform. Operations involved blowing up bridges, railway tracks and ammunition depots, kidnapping persons of prominence, taking prisoners for interrogation purposes and later anti-partisan work.

The recruitment centre was the QM-General Barracks of the former Brandenburg Feld-artillerie Regt at Brandenburg, from which the unit derived its name and which grew to division size during the course of the war. Volunteers, many of them from the Abwehr, were trained at Gut Quenzsee.

In 1941 the Army Weapons Office (Heereswaffenamt) ordered the production of explosive boats similar to the Light Assault Boat 39 built of light spruce. These were the forerunners for the later Linsen of the Kriegsmarine.

In February 1942, Regt Brandenburg zbV 800 set up a maritime unit with the cover name ‘light engineer company’ (Leichte Pionier-kompanie) aboard the sail training brigantine Gorch Fock moored in the Osternot harbour at Swinemünde. Amongst those reporting to the unit were Kriegsmarine small-boat pilots who had carried out landing exercises in the Bansin-Heringdorf area. After successful completion of induction training the company – or individual squads – were deployed in various theatres of war. At the end of 1942 at Langenargen on Lake Constance the Brandenburg coastal infantry unit (Küstenjäger) was formed from the ‘light engineer company’ and other elements from the regiment. The Küstenjäger was composed of four companies, and included the explosive-boat pilots. The Brandenburgers called these ‘explosive speedboats’ (Ladungsschnellboote).

The unit fought under its commander Rittmeister Konrad von Leipzig (a native of German South West Africa, now Namibia) in various theatres of war. The home garrison was Langenargen, the HQ at Schloss Montfort and the boats were kept at nearby Baggersee. In the spring of 1944 the Küstenjäger transferred to the Italian naval base at La Spezia on the Ligurian coast, and in April 1944 were used alongside Neger one-man torpedoes against the Allied bridgehead at Anzio, but achieved no successes. The spruce-built craft found the rough seas very heavy going.

After the K-Verband came into existence, Admiral Heye applied for the boats to come under K-Verband jurisdiction. On 15 April 1944 OKW/Wehrmacht Command Staff ruled in a very wordy piece of prose:

… The operational and tactical conditions of the naval war require uniform operational control of all naval units by the Kriegsmarine. Accordingly, all development work, completion, trials and operations of all special fighting machines (naval) for coastal deployment and at sea are the responsibility of the Kriegsmarine. These machines include in particular special fighting machines (naval) and small fighting machines (naval) as for example one-man boats, remote and wire-controlled explosive-carrying speedboats.

The operational groups for special fighting machines of the OKW/Amt Abwehr or Brandenburg Division which were previously responsible for preparations and operation of special fighting machines (naval) are to be transferred gradually into the Kriegsmarine (Naval Operations Section).

This order does not apply to operations of special fighting machines (naval) on rivers and lakes. Deployment and testing of these boats – insofar as they resemble or are assimilated to boats passing to the Kriegsmarine – is however the responsibility of the Kriegsmarine or is to be carried out jointly with the Kriegsmarine.

As the initial measure, the development and deployment of large explosives-carrying speedboats is to be transferred to the Oberkommando der Marine … and the above mentioned term ‘explosive-carrying speedboat’ is to be understood to mean the Linsen explosive boats.

K-Verband Command took charge of the thirty existing Linsen. Brandenburger Major Goldbach, the inventor and leader of the Linsen units, was transferred into the Kriegsmarine and given the equivalent rank of Korvettenkapitän. All other Küstenjäger were allowed to choose freely between remaining with their unit or transferring into the Kriegsmarine.

The K-Verband soon discovered that the Brandenburger explosive boats were too light for sea service, and an improved Linse was developed by naval designer ObltzS F.H. Wendel, head of the K-Verband Design and Testing Bureau.2 In 1941 Wendel had designed for the Luftwaffe parachute arm a 10-metre long motor boat capable of being dropped into the sea from a Go 242 heavy glider.

The new Linse, more powerful and stable, displaced 1.2 tonnes. It was 5.75 metres in length and was powered by a 3.6-litre Ford 95 hp Otto motor V-8 giving 3,300 revolutions driving two Voith-Schneider propellers. The boat could turn on the spot. Range was 80 sea miles at 15 knots cruising speed. Maximum speed was 31 knots.

The 300 kg (later 480 kg) charge was stowed in four metal containers in the stern of the boat. A metal frame ran around the boat holding a spring 15-cms from the gunwhale. At 80 kgs pressure, the spring activated a timer to detonate the explosive. When a collision occurred with the target ship – the pilot would have jumped off previously – the bow portion was destroyed while the heavy stern section sank with the explosive and motor. By means of a pre-set delay timer the explosive would be detonated after 2.5 or 7 seconds by when the explosives would have reached a depth close to or below the ship’s bottom.

The three-man command boat was equipped with an ultra shortwave transmitter (7-metre band, manufacturer Blaupunkt). The radio beam of the high frequency transmitter was modulated with various low frequency tones. Each tone was an order. The Linse receiver filtered out the tones into relays which translated them into steering orders. An attack Rotte consisted of a command boat and two Linsen. The two command boat crewmen looked after the radio direction equipment while the Rotte-commander picked up the pilots from the water.

The new Linsen were built as from the end of May 1944. By October that year 385 boats had been completed, a total of 1,201 were built altogether. Six to ten yards were involved ranging from Flensburg to East Prussia, for example the Engelbrecht Werft at Berlin Grünau, Elbing and Rostock, also the Kröger Werft at Stralsund, Elbe and Weser. Trials were run mainly on Lake Constance.

On 26 March Kptlt Ulrich Kolbe was transferred from 5 S-boat Flotilla to the K-Verband, and in April 1944 at Lübeck’s Dassower Wik formed K-Flotilla 211 with about ten Linsen. His orders were to work out the tactics and train the personnel. Improvisation was the order of the day, for example there were no trailers to get the Linsen to the beach and into the water. And the radius of action of the boats was only eight sea miles at full speed. This led to the transfer of the flotilla to the barracks of the seaplane base at List on Sylt. Here the weather and sea conditions proved unsuitable for training and another move ensued to the new Lehrkommando 200 at Priesterbeck in Mecklenburg, cover-name Grünkoppel.

The base was the former barracks of a former RAD (Reichsarbeitsdienst) camp in the hamlet of Speck am Specker See whose ten farms were about ten kilometres east of Lake Müritz. The base was hidden away in the Langenhorst Forest, a large nature reserve. In May 1944 the flotilla had a permanent staff and sixty boats were on hand for training after fifty reinforcements arrived by train from Berlin Grünau and from Königsberg in East Prussia.

From July 1944 the head of Lehrkommando 200 was Kptlt Helmut Bastian who had been deprived of his latest command when the torpedo boat Möwe was sunk in the big air raid on Le Havre. Later Lehrkommando 200 was transferred to Plön in Holstein, cover-name Netzkoppel. Bastian had a double function as head of the Lehrkommando and operational leader of the Linse K-Flotillas. In March 1945, after all Linse flotillas had been formed, he took over 4 K-Division, vacant after partisans at Rotterdam assassinated the former encumbent FKpt Josephi.

A Linse flotilla consisted of four groups. Each group had four command boats and eight Linsen. Thus the strength of a Linse flotilla was 16 command boats and 32 Linsen. The attack formation was the pair, or Rotte. On the run towards the enemy, the command boat held the centre position, the two Linsen close in either side so that target and attack details could be shouted across. The pilots were issued lifejackets and later foam-rubber suits for protection against the effects of lengthy immersion in cold waters. A paratrooper helmet was worn. The Linsen were equipped with one-man inflatable dinghies and night rescue lamps. A wrist compass and illuminated chart helped navigation in the event of a return to base.

The Rotte-leader was helmsman of the command boat. His two crew were responsible for controlling the two Linsen after the pilots had jumped out. During the attack each used an ultra short-wave transmitter in a black box balanced on the knees. The remote control operated on different frequencies. By working a lever the Linse would receive the following instructions:

starboard rudder

port rudder

stop engine

start engine

slow ahead

go faster

blow up the boat, if the attack was a failure.

The ultra short-wave device was the steering gear fitted to the German Army’s Goliath, a remote-controlled explosives carrier on tracks used against enemy armoured vehicles, bunkers and other targets.

To outwit enemy defences the Linse had two trumps: speed and manoeuvrability. At night, at the beginning of the attack phase when the pilots could only make out a target as a shadow, their boats would creep up on the enemy ship throttled back to 12 knots so as to avoid premature detection. When the target was confirmed, the Rotte headed full out at 30 knots for the enemy. The pilots checked the course, primed the detonator and switched on the remote control unit. A few hundred metres short of the target they jumped upwards and outwards away from their Linsen. Control of the two boats now passed to the command boat crewmen. At the stern of the pilotless Linse was a green lamp, and a red lamp stood further forward. Both lamps could only be seen from astern. The two lights and the target had to be aligned for a hit.

Once the attack terminated a search would be made for the Linse pilots in the water. Their lifejackets would have a small lamp to aid this endeavour. As soon as the pilots were aboard the command boat it would turn away at full speed and within seconds lay a 30-metre broad smoke screen from a stern installation. That was the theory, the practice would often turn out to be more complicated.

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