The Marinefährprähme (MFP, naval ferry barges) had been developed as a direct result of the aborted Operation Sealion. Preparations for the invasion of Great Britain had starkly highlighted the lack of suitable landing craft, forcing a reliance on hastily- converted civilian barges. All branches of the Wehrmacht were invited to submit proposals for landing craft designs, the Luftwaffe developing the Siebel Fähre (Siebel ferry, named after its creator, aircraft designer Luftwaffe Oberst Fritz Siebel) constructed of two bridgebuilding pontoons connected by a platform with BMW aircraft engines mounted astern for propulsion. The remainder of the platform carried the payload; vehicles were able to embark and disembark via a bow ramp. Constructed in moderate quantities, variants were built that carried artillery, headquarters facilities and field hospitals.
Meanwhile, Kriegsmarine experimentation had resulted in a list of requirements for a vessel capable of being used either a landing craft or supply vessel. It needed to be cheap to construct, have a retractable bow ramp, a large carrying capacity and the ability to operate in sea state 5 (wave height of 3m). The resultant 155-ton design incorporated all of these features, constructed of riveted steel with a raised stern and bow complete with ramp. The aft portion of the cargo area was enclosed by a steel roof giving a maximum clearance of 2.74m, the forward section featuring removable corrugated iron shutters. Three six-cylinder deutz diesel truck engines were placed in a stern engine room above which the wheelhouse was mounted, both protected by 20mm-25mm armour plating. The craft could make 10.5 knots but were found to be only able to manage sea state 2 at full load. Marinefährprähme were equipped with MES mine defence which interfered with magnetic compass navigation, requiring pilot boats to guide them in operation. At first they were equipped with two 20mm flak but, like most Kriegsmarine security vessels, they would be considerably up-gunned as the war progressed. The original crew complement was two officers and ten men.
Highly successful, MFPs were built in over a dozen different shipyards in both Germany and occupied territories, resulting in a wide range of modifications to the general design. The initial model became known as `Type A’, three variants following:
Type B, where the load floor was lowered to provide a cargo area clearance of 3.19m;
Type C, with an additional 10cm added to the height odf the cargo area;
Type D, with the fully-riveted construction changed to partially welded. The hull was lengthened and widened and the carrying capacity increased to 140 tons, capable of accommodating a Tiger I heavy tank. The wheelhouse and engine room were moved slightly forward with reinforced armour and weaponry added, particularly for defence against aircraft. By this stage, the crew had also increased to a standard twenty-five men.
Additionally, like its Luftwaffe counterpart, different requirements resulted in specific variants as the war progressed and their employment frequently became more akin to that of the Vorpostenboote. Three MFPs were converted into hospital vessels, four into tankers, four into repair ships, forty into dedicated minesweepers or Sperrbrecher and one into a U-Jäger; UJ118. The dedicated Minenfährprähm were used primarily in the Adriatic and the Black Sea, carrying anywhere between thirty-six and fifty-four mines depending on the variant; the mines were loaded via the front ramp on installed rails and dropped over the stern. Alternatively, if the situation required retasking, the rails could carry sixteen Sturmboot for infantry amphibious landings.
Additionally, 141 were permanently converted into gunboats (Artilleriefährprähme). This was achieved by fitting armament consisting of two 88mm and one 75mm gun and two 20mm Vierling. The cargo hold was converted into a magazine protected by armour 100mm thick, bolstered by 10cm of concrete filling the adjacent bulwarks. The overall increase in weight reduced the Artilleriefährprähme’s maximum speed to 8 knots. The crew quarters were also enlarged to accommodate the extra gunners. Of shallow draught, they became extremely effective in inshore waters, operating in Northern Europe, the Black Sea (all such vessels had their pennant numbers prefixed `AF’), within the Mediterranean (`KF’) and on the Danube (`AT’).
In December 1941, it had become apparent that many MFPs would be required for transport and supply operations in the Black Sea and the Aegean; the Allied submarine menace was guaranteed to increase rather than decrease while there would be little opportunity to bolster German ASW defences. For this reason, barges were considered the safest and most suitable means of transport, requiring no escort and the risk of loss of materiel and personnel in each case being relatively small. Schuster proposed that Von Stotsch at once order the construction of fifty MFPs, the best building facility being found in Palermo. As SKL recorded, it was likely that `the Seelöwe will be asleep for quite a while’ and the barges were not needed in France. By the end of 1941 three more Küstenschutzflottillen had been established in the Aegean; the 11th at Mudros, the 12th at Piraeus and the 13th at Suda in Crete. All three flotillas comprised the same basic sub-division of vessel types as Peters’ flotilla in Thessaloniki. Apart from these auxiliary units, the first unit of the Kriegsmarine Security Forces to serve in the Mediterranean was the 21st UJ-Flotilla, patrolling the waters between the Dardanelles and Crete. Based in Piraeus, the flotilla was commanded by FK Günther von Selchow who had successfully led the 11th UJ-Flotilla since the outbreak of war. Coupled with the, requisitioned U-Jäger, von Selchow would also control the minelayers Bulgaria, Drache and Zeus as well as the auxiliary minelayers Otranto, Alula and Gallipoli.