Major Fritz Siebel and Fieldmarshall Albert Kesselring tour the Siebelferry of Ernst Grossmann on December 11, 1941

Sonderkommando Siebel

In the summer and autumn of 1940, Wachtmeister Ernst Großmann was stationed in Antwerp as his unit prepared for Unternehmen Seelöwe (Operation Sealion), the planned German invasion of England. As the Luftwaffe prepared its aircraft for the Battle of Britain, it also fell to the Luftwaffe to take a critical role in the physical seaborne invasion. Surprisingly, it was not the Kriegsmarine that developed, deployed, and manned the first operational German amphibious invasion force. It was the Luftwaffe.

The makeshift German invasion fleet practices for the invasion of England. A hodgepodge of Siebelferries, river barges, tugs, and ships were cobbled together for Operation Sealion.

Sealion's Ships

"Invasion Ferries"

In September, Ernst Großmann's unit, Flak Abteilung 253 (by December absorbed into Flak Abteilung 402), kitted out its first "invasion ferries" in Antwerp, at the Leopolddok on the River Scheldt, with these ferries then being stationed in ports including Calais, Ostend, and Zeebrugge. From these locations, the craft conducted invasion drills, seafaring tests, minesweeping, minelaying, fuel supply, and anti-aircraft operations through to 1941, at which point they were redeployed to other fronts. Eventually, hundreds of these craft were built and deployed to the Baltic, Black Sea, Lake Ladoga, the Mediterranean, and to numerous rivers where they fought and ferried troops and equipment, the ferries becoming some of the only vehicles used by all three branches of the Wehrmacht. This, then, is the story of how a Luftwaffe officer's serendipitous meeting with an army engineer officer led to the creation of Germany's most successful amphibious craft: the Siebel Ferry.

A heavy Flak Siebelferry from 2nd Batterie 253rd Flak Abteilung (later 402nd) in Zeebrugge

The cost of Operation Weserübung

The story of Germany's amphibious forces in the Second World War is one of necessity, trial, and error. Being a land power, Germany lacked dedicated landing craft at the start of the conflict and had to cobble equipment together from available resources. This was evident during Operation Weserübung, the invasion of Norway, where the Kriegsmarine relied on the surface fleet for speed and surprise. Instead of using transports and landing craft, troops were moved on destroyers and minesweepers to unload directly in ports, while larger ships like the cruiser Admiral Hipper used small launches to disembark men.

While the Norway operation succeeded, it decimated the Kriegsmarine, which lost a heavy cruiser, two light cruisers, and ten destroyers. These losses severely hampered preparations for Operation Sealion. Although feasibility studies began in November 1939, Hitler only reviewed the proposal in June 1940. Initially unimpressed, he eventually shifted his stance, formalizing the strategy in Führer Directive No. 16. The plan involved two army groups attacking in waves to secure a bridgehead on the English coast, supported by airborne units and cover from the Luftwaffe and Kriegsmarine.

Enter "Fritz" Siebel

Despite these ambitious plans, the German military faced a daunting reality: they lacked the shallow-draft vessels necessary to challenge the massive Royal Navy in the English Channel. The specialized amphibious force required for a cross-channel invasion simply did not exist in 1940. To bridge this gap, the military had to look for innovative, unconventional solutions to transport men and armor across the water. This dire lack of equipment set the stage for a new phase of rapid development and improvisation, leading to the entrance of an unlikely figure in German naval history: Fritz Siebel.

On 1 May 1940, Luftwaffe Major Friedrich 'Fritz' Siebel, an aircraft designer by trade, was placed in charge of aircraft maintenance facilities near Amiens where he was approached by the commander of an engineering unit in the area requesting surplus aircraft fuel tanks for the construction of rafts to be used in the invasion of England. Siebel, dubious of the seaworthiness of the proposed rafts, began to investigate other options. Although he was not the only one working on efforts to solve the landing craft problem, his eventual design ended up being the most capable.

Fieldmarshal Albert Kesselring speaks to Major Fritz Siebel on the stern of a Siebelferry from Flak Abteilung 402 departing Antwerp for the Channel Coast.

Building an amphibious force

Frustrated by the lack of landing craft, the Wehrmacht planned to convert inland river barges and numerous makeshift types were under development in July 1940. At about that time, Siebel learned that Pioneer Battalion 47 had begun to construct reinforced ferries from bridging equipment on the banks of the Somme in Bray-sur-Somme and successfully demonstrated them to the General of Pioneers on 25 July 1940. However, these proved underpowered and not particularly seaworthy. Given the conditions often prevailing in the English Channel, it would not do to lose the invasion force to a squall.

Another solution needed to be found, and in Antwerp, Siebel found bridge-building battalions crafting makeshift ferries from heavy bridge pontoons. Their main problem, though, was propulsion. And this was something aircraft designers knew about! At that time, the Luftwaffe had an abundant supply of BMW VI aircraft engines that had been used in early variants of aircraft like the Dornier 17-E. By 1940, these water-cooled V12 engines were no longer suitable for combat aircraft, but Siebel realised they would be perfect if they could be mounted on pontoon barges. In the First World War, he had been on the staff with Ernst Udet who later became Air Minister, and he used his connections with Udet to push his plan and approached the office of the Chief of Supply of the Luftwaffe. In turn, his recommendation was forwarded to the Oberkommando der Luftwaffe.

The plan was to create a new type of auxiliary amphibious vessel, based on catamaran pontoon barges by using heavy bridging pontoons that were readily available and then have them mated to customised superstructures and powered by the BMW VI. The recommendation was approved, the Luftwaffe launching Sonderkommando Siebel (Siebel Special Command) with two officers, a chief engineer, an inspector, and 180 NCOs and enlisted men. According to Siebel's post-war interrogation report, the unit was launched at the beginning of July 1940 in Antwerp.

The Wehrmacht practiced beach landings off the coast of Midsland in the West Frisian Islands in the late summer and early autumn of 1940. It is difficult to believe anyone in the German military thought they could successfully assault English beaches.

Fähre-Sonderkommando

Sonderkommando Siebel was eventually re-named Fähre-Sonderkommando, Ferry Special Command, located in the present-day Antwerp Maritime Academy, it was tasked with producing large numbers of seaworthy landing craft capable of multiple transits of the English Channel. Though they worked in concert with engineers from the army's Engineer Ferry Construction Command 1, led by Major Böndel in Antwerp, the ferries would be named after their original patron: Major Siebel. The craft were to be capable of ferrying hundreds of soldiers and equipment as they plied to-and-fro, with some variants armed with 88mm guns to protect the flotilla. Each ferry, though, could carry 50 infantrymen and their equipment, plus a howitzer or a light tank. The operational concept for the Siebel ferries, as well as the unpowered barges, required a massive number of tugs that would tow landing craft to the English coast, releasing them under their own power for the final assault. The craft would then beach themselves, unload men and material, and return to the tugs which would ferry the now empty craft to France and Belgium to reload for a second and third wave. The Luftwaffe also organised two flotillas to provide flak guns as defence against destroyers and aircraft to the first wave: Flakkorps I was assigned to 9th Army (covering western landing zones) and Flakkorps II was assigned to 16th Army (covering eastern landing zones).

A ferry tows a transport version of the Siebelferry carrying several e-ton Opel Blitz trucks, soldiers, and their equipment. The number of tugs Germany would have needed to invade England were staggering.

Testing

Testing the craft took place in July on the Ems estuary and on Rangsdorfer See, a lake near Berlin, with great interest being shown in the Siebel concept within Oberkommando des Heeres (OKH), the army high command. Concerned as to how they would get their soldiers to English beaches without navy ships, Field Marshal von Brauchitsch, Supreme Commander of the German Army, attended the tests along with General Franz Halder, chief of staff of the OKH, General Jakob, the General of Engineers, and General Ernst Udet, the Luftwaffe's head of rearmament. This must have been a defining moment in Major Siebel's career, and luckily the tests went well with Siebel instructed to begin production on this and other improved models with haste.

Siebel began work immediately; the initial production being in St. Omer with the first batch of transport ferries simply called Kleinefähre, or small ferries. These basic craft used surplus outboard BMW VI aircraft engines with propellers built on mounts above the main deck to provide propulsion. This airscrew propulsion proved problematic due to high suction, leading to several deaths. Reinforced with protective grilles, they were still so loud that voice commands on the ferries were inaudible. Thus, these engines would only be used for the final assault. Additionally, the noise of the engines would have quickly attracted British attention had they been used directly from the point of setting sail. Not only that, but there would surely have been engine cooling problems during the crossing itself.

A so-called "B-Type" Kleinefähre sits in the Leopolddok, Antwerp in 1940. The large outboard BMW engines are clearly visible. In total, 150 of the ferries were constructed in short order. However, they were insufficient to transport the heavy equipment and large numbers of soldiers needed for the invasion; for this, the Sonderkommando developed a new craft that would become known as the Siebel Ferry 40.

Technical Specifications for the SF 40

A heavy flak SF 40 loading it's 88mm guns in Antwerp. These ferries were supposed to take on the English destroyers with direct fire as well as protect from airborne threats. It was something of a fantasy.

Crew: 10
Length: 24.25m
Width: 13.70m
Draft: 1.20m
Capacity: 100 tons
Propulsion: Initially, four inboard Diesel Ford V8 Engines, some variants supplemented by two to three (depending on variant) BMW VI aircraft engines mounted above the main deck with aircraft propellers. Final production SF 40 dispensed with outboard engines, using inboard BMW aircraft engines with reversing gear.
Speed: 8-11 kts (depending on type)
Range: 570km
Note: Each Siebel Ferry was identified by number, but it was not uncommon for the crew to give the vessels names and artistic logos, much like aircraft nose art. Some names noted in photographs and other sources include: Shark, Dolphin, Pike, Mackerel, and Loch Ness.

The Siebel Ferry 40 (SF 40), then, were catamaran pontoon boats composed of multiple flat-bottomed and enclosed rectangular pontoons made from 4mm sheet metal, the complete units manufactured by Krupp-Stahlbau Rheinhausen, a bridge construction company in the Lower Rhine near Duisburg. Six pontoons formed each of the two-part body, and another two were slanted at an angle, fore and aft, to allow the craft to be beached for unloading. The two main floats were placed six metres apart, connected by heavy iron bars and covered with corrugated planks 6cm thick, in turn covered with wooden planking. There was a central deckhouse where steering control was located, and on which various anti-aircraft defences and other equipment were mounted, depending on the type. Each ferry had a ten-man crew, but without onboard accommodation, the men had to be housed ashore when not at sea.

Sealion Postponed

With the Luftwaffe failing to quickly defeat England in the Battle of Britain and with the Blitz in full swing, Sea Lion was postponed that September. It was unclear whether the Luftwaffe would be able to provide protection for an invasion due to mounting losses, and without operational landing craft, Sealion could not go forward, anyway. Time had now also run out due to impending autumnal weather that would make any crossing perilous, and as the reality of the operation's scale becoming clearer the impending invasion of Russia in 1941 took precedence. Still, postponed doesn’t mean cancelled, and so preparations continued.

Newly promoted Feldmarschall Albert Kesselring travelled to Antwerp to meet with Major Siebel and inspect his work on December 11, 1940. At this time, Ernst Großmann operated the Entfernungsmesser, or rangefinder, for an 88mm anti-aircraft battery on one of the first heavy flak Siebel Ferries. He was part of Flak Abteilung 253, a unit formed in Heilbronn with men from the Stuttgart region. That unit initially fielded some of the invasion ferry flak units but by December of 1940 it was integrated into Flak Abteilung 402 where Großmann was part of the Sealion invasion force. Major Siebel and the Field Marshall took up position on Ernst's Heavy Flak ferry to observe the exercise, while numerous transport variants of the SF 40 were fully loaded with men and material and escorted by heavy flak SF 40s. Each of the latter were equipped with four 88mm anti-aircraft artillery pieces. Kesselring was impressed by what he saw, and so long as the sea state was at four or less, then Siebel Ferries were more than capable of transiting the Channel.

On January 13, 1941 Ernst Großmann took this photo through a rangefinder from his Siebelferry while about 8 miles from the White Cliffs of Dover during an exercise.

Further Developments

Luftwaffe men found their sea legs and became sailors. They conducted coastal patrols and engaged RAF bombers, with minelaying and minesweeping a common duty. In fact, it was not unusual for a Luftwaffe flak gunner to earn the Navy's minesweeping badge before earning his anti-aircraft badge! (see photo right)

A redesign in 1943 led to a longer hull and an all-metal two-story deck house that could be moved fore or aft as required. This provided a more robust ferry for the intense late-war combat, but only 18 were delivered by 14 September 1944, with all further orders cancelled. A final variant, the SF 44, was developed in 1944 with a wheelhouse placed forward of the main deck house, but only one prototype was delivered in February 1945.

However, the craft designed to mount a seaborne invasion of Britain was never put to that use or tested in its intended capacity, although author Peter Schenk notes in his book Operation Sealion, The Invasion of England 1940, that: "They were the only 'real' landing craft in the Sealion fleet".

Luftwaffe Siebelferry crew on the Channel Coast. Note many of them bear the Minesweeper badge, an award typically given to members of the German Navy. They also lack the Flak badge for engaging aircraft.

Post Sealion Applications

There was great interest in the SF 40, and they continued to operate in the Channel.By the end of September 1940, some 27 production SF 40 had been completed, ferried to Antwerp, and kitted out for the invasion force which was still waiting for Sealion. Among them was a mix of transport and heavy flak variants in the first batch, the ferries being so well-received that an immediate order for an additional 200 was issued to Krupp-Stahlbau Rheinhausen. Regular Siebel Ferry operations in the Channel finally commenced in October 1940, operating from Calais, Dunkirk, Ostend, Zeebrugge, and other ports.

Some 400 ferries were built during the war, with Channel operations continuing well into 1941. On 23 September 1941, though, all Sealion preparations finally ceased, just over a year since the Siebel Ferry was fielded in Antwerp. Easily shipped via rail, and with good seaworthiness, they saw widespread use by the Wehrmacht. They first saw combat in the summer of 1941 in the Black Sea and were widely used on Lake Ladoga, Italy, and in North Africa.

In 1942 the Luftwaffe created 5 regional ferry flotillas, or Luftwaffen-Fähren Flottille, that used Siebel ferries to transport troops and material. They were:

Luftwaffen-Fährenflotille 1 operated 12 Siebel ferries and were transferred from the Channel to the Kertsch strait.
Luftwaffen-Fährenflotille 2 & 3 operated on Lake Ladoga in northern Russia with 23 Siebel ferries until transferred to the Mediterranean at the end of 1942.
Luftwaffen-Fährenflotille 4 & 5 operated between Sicily and North Africa and had 97 Siebel ferries - the most operating in any single location.

Siebel himself rose to the rank of Colonel, spending the remainder of the war working with the ferries he helped design. He traveled to Finland and Lake Ladoga where he commanded Einsatzstab Fähre Ost, drawing heavily on men and materiel from the Channel ferry units. The unit operated seven heavy flak ferries, six light flak ferries, six transport, six repair craft, a hospital, and one HQ ferry.

The ferries had become so versatile by 1941, that their uses far outstripped the plans first envisioned for Operation Sealion, seeing widespread use in North Africa, Italy, Corsica, and Sardinia. For example, then Oberst Siebel wrote how his ferries evacuated over 4,000 soldiers and thousands of tons of equipment from Corsica in 1943. Ironically, Siebel was captured by British forces in 1945, with the man who spent so much time working out how to get to England finally captured by its soldiers. After the war, Siebel founded an aircraft company called Siebel Flugzeugwerke ATG but died on 24 April 1954. His company was eventually absorbed by Messerschmitt-Bölkow-Blohm, currently part of Airbus.