Editing Operation Sea Lion (section)

== Navy ==
[[File:D.Adm.66 Der Kanal Ost Blatt by www.kartengruppe.it.jpg|thumb|left|The Channel (Der Kanal), D.66 ''Kriegsmarine'' nautical chart, 1943]]
The most daunting problem for Germany in protecting an invasion fleet was the small size of its navy. The ''Kriegsmarine'', already numerically far inferior to Britain's Royal Navy, had lost a sizeable portion of its large modern surface ships in April 1940 during the Norwegian campaign, either as complete losses or due to battle damage. In particular, the loss of two light cruisers and ten destroyers was crippling, as these were the very warships most suited to operating in the Channel narrows where the invasion would likely take place.<ref name="Von der Porten111">Von der Porten, p. 111</ref> Most [[U-boat]]s, the most powerful arm of the {{lang|de|Kriegsmarine}}, were meant for destroying ships, not supporting an invasion.

Although the Royal Navy could not bring the whole of its naval superiority to bear{{snd}}as most of the fleet was engaged in the [[Atlantic Ocean|Atlantic]] and [[Mediterranean Sea|Mediterranean]], and a substantial proportion had been detached to support [[Battle of Dakar|Operation Menace]] against [[Dakar]]{{snd}}the British Home Fleet still had a very large advantage in numbers. It was debatable whether British ships were as vulnerable to enemy air attack as the Germans hoped. During the [[Operation Dynamo|Dunkirk evacuation]], few warships were actually sunk, despite being stationary targets. The overall disparity between the opposing naval forces made the amphibious invasion plan extremely risky, regardless of the outcome in the air. In addition, the ''Kriegsmarine'' had allocated its few remaining larger and more modern ships to diversionary operations in the North Sea.

The fleet of defeated France, one of the most powerful and modern in the world, might have tipped the balance against Britain if it had been captured by the Germans. However, the pre-emptive destruction of a large part of the French fleet by the British [[Attack on Mers-el-Kébir]] on 3 July 1940 ensured that this could not happen.

Those who believed that, regardless of a potential German victory in the air battle, Sea Lion was still not going to succeed included a number of German General Staff members. After the war, Admiral [[Karl Dönitz]] said he believed air superiority was "not enough". Dönitz stated, "[W]e possessed neither control of the air or the sea; nor were we in any position to gain it".<ref>Dönitz 1958 (1997 edition), p. 114.</ref> In his memoirs, Raeder, commander-in-chief of the ''Kriegsmarine'' in 1940, wrote:
{{blockquote|[U]p until now the British had never thrown the full power of their fleet into action. However, a German invasion of England would be a matter of life and death for the British, and they would unhesitatingly commit their naval forces, to the last ship and the last man, into an all-out fight for survival. Our Air Force could not be counted on to guard our transports from the British Fleets, because their operations would depend on the weather, if for no other reason. It could not be expected that even for a brief period our Air Force could make up for our lack of naval supremacy.<ref>Raeder 2001, pp. 324–25.</ref>}}

On 13 August 1940, Jodl, Chief of Operations in the [[OKW]] (''Oberkommando der Wehrmacht'') wrote his "Assessment of the situation arising from the views of the Army and Navy on a landing in England." His first point was that "The landing operation must under no circumstances fail. A failure could leave political consequences, which would go far beyond the military ones." He believed that the ''Luftwaffe'' could meet its essential objectives, but if the ''Kriegsmarine'' could not meet the operational requirements of the Army for an attack on a broad front with two divisions landed within four days, followed promptly by three further divisions irrespective of weather, "then I consider the landing to be an act of desperation, which would have to be risked in a desperate situation, but which we have no reason whatsoever to undertake at this moment."{{sfn| Evans| Mcgeoch|2014|pp=87–88}}

===Deception===
The ''Kriegsmarine'' invested considerable energy in planning and assembling the forces for an elaborate [[military deception|deception]] plan called [[Operation Herbstreise]] or "Autumn Journey". The idea was first mooted by ''[[Generaladmiral]]'' [[Rolf Carls]] on 1 August proposing a [[feint]] expedition into the North Sea resembling a troop convoy heading for Scotland, with the aim of drawing the British Home Fleet away from the intended invasion routes. Initially, the convoy was to consist of about ten small [[cargo ship]]s fitted with false funnels to make them appear larger, and two small [[hospital ship]]s. As the plan gathered momentum, the large [[ocean liner]]s {{SS|Europa|1928|2}}, {{SS|Bremen|1928|2}}, {{SS|Gneisenau|1935|2}} and {{SS|Potsdam|1935|2}} were added to the list. These were organised into four separate convoys, escorted by light cruisers, torpedo boats and minesweepers, some of which were obsolete vessels being used by naval training bases. The plan was that three days before the actual invasion, the troopships would load the men and equipment of four divisions in major Norwegian and German ports and put to sea, before unloading them again on the same day in quieter locations. Returning to sea, the convoys would head west towards Scotland before turning around at about 21:00 on the following day. In addition, the only heavy warships available to the ''Kriegsmarine'', the heavy cruisers {{ship|German cruiser|Admiral Scheer||2}} and {{ship|German cruiser|Admiral Hipper||2}}, would attack the British [[Armed merchantman#Armed merchant cruisers|armed merchant cruisers]] of the [[Northern Patrol]] and convoys inbound from Canada; however, the ''Scheer'''s repairs overran and if the invasion had taken place in September, would have left the ''Hipper'' to operate alone.<ref>Schenk, pp. 319–21</ref>

=== Minefields ===
Lacking surface naval forces capable of meeting the Home Fleet of the Royal Navy in open battle, the main seaborne defence for the first wave invasion fleets would have been four massive minefields, which were intended to be laid from S minus nine, thus nine days before landing. The ANTON minefield (off [[Selsey Bill]]) and the BRUNO minefield (off Beachy Head), each totalling over 3,000 mines in four rows, would have blocked off the invasion beaches against naval forces from Portsmouth, while the counterpart CAESAR minefield would have blocked off beach 'B' from Dover. A fourth minefield, DORA, was to be laid off [[Lyme Bay]] to inhibit naval forces from [[Plymouth]]. By the autumn of 1940, the ''Kriegsmarine'' had achieved considerable success in laying minefields in support of active operations, notably in the night of [[Texel Disaster|31 August 1940]] when the 20th Destroyer flotilla suffered heavy losses when running into a newly laid German minefield near the Dutch coast off [[Texel]]; however no plans were made to prevent the mines being cleared by the large force of British [[minesweeper]]s which were based in the area. ''[[Vizeadmiral]]'' [[Friedrich Ruge]], who was in charge of the mining operation, wrote after the war that if the minefields had been relatively complete, they would have been a "strong obstacle" but that "even a strong obstacle is not an absolute barrier."<ref>Schenk pp. 330–32</ref>

=== Landing craft ===
[[File:Bundesarchiv Bild 101II-MN-1369-10A, Wilhelmshaven, Prahme für "Unternehmen Seelöwe".jpg|thumb|Invasion barges assembled at the German port of [[Wilhelmshaven]].]]
In 1940 the German Navy was ill-prepared for mounting an amphibious assault the size of Operation Sea Lion. Lacking purpose-built landing craft and both doctrinal and practical experience with amphibious warfare, the ''Kriegsmarine'' was largely starting from scratch. Some efforts had been made during the inter-war years to investigate landing military forces by sea, but inadequate funding severely limited any useful progress.<ref name=Schenk22-25>Schenk, pp. 22–25</ref>

For the successful German invasion of Norway, German naval forces (assisted in places by thick fog) had simply forced an entry into key Norwegian harbours with motor launches and [[E-boats]] against stiff resistance from the outgunned Norwegian army and navy, and then unloaded troops from destroyers and troop transports directly onto the dockfronts at [[Bergen]], [[Egersund]], [[Trondheim]], [[Kristiansand]], [[Arendal]] and Horten.{{sfn|Forczyk|2016|p=71}} At [[Stavanger]] and [[Oslo]] capture of the port was preceded by landing airborne forces.  No beach landings were attempted.

The ''Kriegsmarine'' had taken some small steps in remedying the landing craft situation with construction of the ''[[Pionierlandungsboot 39]]'' (Engineer Landing Boat 39), a self-propelled shallow-draft vessel which could carry 45 infantrymen, two light vehicles or 20 tons of cargo and land on an open beach, unloading via a pair of clamshell doors at the bow. But by late September 1940 only two prototypes had been delivered.<ref name=Schenk29>Schenk, p. 29</ref>

Recognising the need for an even larger craft capable of landing both tanks and infantry onto a hostile shore, the ''Kriegsmarine'' began development of the 220-ton ''[[Marinefährprahm]]'' (MFP) but these too were unavailable in time for a landing on British soil in 1940, the first of them not being commissioned until April 1941.

[[File:Bundesarchiv Bild 101II-MN-2781-19, Russland, Landungsboot mit Zugkraftwagen.jpg|thumb|left|A Pionierlandungsboot]]

Given barely two months to assemble a large seagoing invasion fleet, the ''Kriegsmarine'' opted to convert inland river barges into makeshift landing craft. Approximately 2,400 barges were collected from throughout Europe (860 from Germany, 1,200 from the Netherlands and Belgium and 350 from France). Of these, only about 800 were powered albeit insufficiently to cross the Channel under their own power. All barges would be towed across by tugs, with two barges to a tug in line abreast, preferably one being powered and one unpowered.  On reaching the English coast, the powered barges would be cast-off, to beach themselves under their own power; the unpowered barges would be taken inshore as far as possible by the tugs and anchored, so as to settle on the falling tide, their troops unloading some hours later than those on the powered barges.<ref name=Schenk67>Schenk, p. 67</ref>  Accordingly, the Sea Lion plans were prepared on the basis that the landings would take place shortly after high tide and on a date when this coincided with sunrise. Towards evening, on the following rising tide, the empty barges would have been retrieved by their tugs to receive the second echelon forces, stores and heavy equipment in the awaiting transport vessels. These transport vessels would have remained moored off the beach throughout the day.  By contrast, the Allied [[D day]] landings in 1944 were timed to happen at low tide; with all troops and equipment transhipped from their transport vessels to landing craft off-shore overnight.

All the troops intended to land at beach 'E', the westernmost of the four beaches, would cross the channel in larger transport vessels – the barges being towed loaded with equipment but empty of troops – and would then be transferred onto their barges a short distance from the beach.  For the landings on the other three beaches, the first echelon of the invasion forces (and their equipment) would be loaded onto their barges in French or Belgian ports, while the second echelon force crossed the channel in associated transport vessels. Once the first echelon had been unloaded onto the beach, the barges would return to the transport vessels to transport the second echelon. The same procedure was envisaged for the second wave (unless the first wave had captured a usable port). Trials showed that this process of trans-shipment in open sea, in any circumstances other than flat calm, would likely take at least 14 hours,{{sfn|McKinstry|2014|p=307}} such that the disembarkation of the first wave might extend over several tides and several days, with barges and invasion fleet subsequently needing to be escorted together back across the Channel for repairs and reloading. Since loading of the tanks, vehicles and stores of the second wave onto the returned barges and transport ships would take at least a week, the second wave could not be expected to land much less than ten days after the first wave, and more likely longer still.{{sfn|Forczyk|2016|p=249}}

==== Barge types ====
Two types of inland river barge were generally available in Europe for use in Sea Lion: the ''peniche'', which was 38.5 meters long and carried 360 tons of cargo, and the ''Kampine'', which was 50 meters long and carried 620 tons of cargo. Of the barges collected for the invasion, 1,336 were classified as ''peniches'' and 982 as ''Kampinen''. For simplicity's sake, the Germans designated any barge up to the size of a standard ''peniche'' as Type A1 and anything larger as Type A2.<ref name=Schenk65-74>Schenk, pp. 65–74</ref>

==== Type A ====
Converting the assembled barges into landing craft involved cutting an opening in the bow for off-loading troops and vehicles, welding longitudinal I-beams and transverse braces to the hull to improve seaworthiness, adding a wooden internal ramp and pouring a concrete floor in the hold to allow for tank transport. As modified, the Type A1 barge could accommodate three medium tanks while the Type A2 could carry four.<ref name=Schenk99>Schenk, p. 99</ref> Tanks, armoured vehicles and artillery were envisaged as crossing the Channel in one of around 170 transport ships, which would be anchored off the landing beaches while the barges disembarked the first echelon of assault troops; those in powered barges disembarking soonest.  The empty barges would then have been retrieved by tugs on the following rising tide, so as to have the second echelon (including tanks and other heavy equipment) loaded onto them using ship's [[derrick]]s. Barges would consequently have shuttled between ships and beaches over at least two days before being assembled together for the escorted night-time return voyage across the Channel.

==== Type B ====
This barge was a Type A altered to carry and rapidly off-load the submersible tanks (''Tauchpanzer'') developed for use in Sea Lion. They had the advantage of being able to unload their tanks directly into water up to {{convert|15|m|ft|0}} in depth, several hundred yards from shore, whereas the unmodified Type A had to be firmly grounded on the beach, making it more vulnerable to enemy fire. The Type B required a longer external ramp (11 meters) with a float attached to the front of it. Once the barge anchored, the crew would extend the internally stowed ramp using block and tackle sets until it was resting on the water's surface. As the first tank rolled forward onto the ramp, its weight would tilt the forward end of the ramp into the water and push it down onto the seabed. Once the tank rolled off, the ramp would bob back up to a horizontal position, ready for the next one to exit. If a barge was securely grounded along its full length, the longer ramp could also be used to discharge submersible tanks directly onto the beach, and beachmasters were given the option of landing tanks by this method, if the risk of loss in submersible running appeared to be too high.  The Navy High Command increased its initial order for 60 of these vessels to 70 in order to compensate for expected losses. A further five were ordered on 30 September as a reserve.<ref name=Schenk99-105>Schenk, pp. 99–105</ref>

==== Type C ====
The Type C barge was specifically converted to carry the [[Panzer II]] amphibious tank (''Schwimmpanzer''). Because of the extra width of the floats attached to this tank, cutting a broad exit ramp into the bow of the barge was not considered advisable as it would have compromised the vessel's seaworthiness to an unacceptable degree. Instead, a large hatch was cut into the stern, thereby allowing the tanks to drive directly into deep water before turning under their own motive power and heading towards shore. The Type C barge could accommodate up to four ''Schwimmpanzer'' in its hold. Approximately 14 of these craft were available by the end of September.<ref name=Schenk105-107>Schenk, pp. 105–07</ref>

==== Type AS ====
During the planning stages of Sea Lion, it was deemed desirable to provide the advanced infantry detachments (making the initial landings) with greater protection from small-arms and light artillery fire by lining the sides of a powered Type A barge with concrete. Wooden slides were also installed along the barge's hull to accommodate ten assault boats (''Sturmboote''), each capable of carrying six infantrymen and powered by a 30&nbsp;hp outboard motor. The extra weight of this additional armour and equipment reduced the barge's load capacity to 40 tons. By mid-August, 18 of these craft, designated Type AS, had been converted, and another five were ordered on 30 September.<ref name="Schenk99" />

==== Type AF ====
The ''Luftwaffe'' had formed its own special command (''Sonderkommando'') under Major Fritz Siebel to investigate the production of landing craft for Sea Lion. Major Siebel proposed giving the unpowered Type A barges their own motive power by installing a pair of surplus {{convert|600|hp|kW|abbr=off|adj=on}} BMW aircraft engines, driving propellers. The ''Kriegsmarine'' was highly sceptical of this venture, but the ''Heer'' (Army) high command enthusiastically embraced the concept and Siebel proceeded with the conversions.<ref name=Schenk94-98>Schenk, pp. 94–98</ref>

The aircraft engines were mounted on a platform supported by iron scaffolding at the aft end of the vessel. Cooling water was stored in tanks mounted above-deck. As completed, the Type AF had a speed of {{convert|6|kn|km/h|spell=in|0}}, and a range of {{convert|60|nmi|km|abbr=off|round=5}} unless auxiliary fuel tanks were fitted. Disadvantages of this set-up included an inability to back the vessel astern, limited manoeuvrability and the deafening noise of the engines which would have made voice commands problematic.<ref name="Schenk94-98" />

By 1 October 128 Type A barges had been converted to airscrew propulsion and, by the end of the month, this figure had risen to over 200.<ref name=Schenk95>Schenk, p. 95</ref>

The ''Kriegsmarine'' later used some of the motorised Sea Lion barges for landings on the Russian-held Baltic islands in 1941 and, though most of them were eventually returned to the inland rivers they originally plied, a reserve was kept for military transport duties and for filling out amphibious flotillas.<ref name=Schenk94>Schenk, p. 94</ref>

===Escort===
As a consequence of employing all of their available cruisers in the North Sea deception operation, there would have been only light forces available to protect the vulnerable transport fleets. The plan revised on 14 September 1940 by Admiral [[Günther Lütjens]] called for three groups of five U-boats, all seven destroyers, and seventeen [[torpedo boat]]s to operate to the west of the mine barrier in the Channel, while two groups of three U-boats and all the available [[E-boat]]s to operate north of it.<ref>Schenk, pp. 335–37</ref> Lütjens suggested the inclusion of the old battleships {{SMS|Schlesien}} and {{SMS|Schleswig-Holstein}} which were used for training. They were considered too vulnerable to send into action without improvement, especially considering the fate of their sister ship, {{SMS|Pommern}}, which had blown up at the [[Battle of Jutland]]. The [[Blohm und Voss]] shipyard considered that it would take six weeks for a minimal upgrade of armour and armament and the idea was dropped, as was a suggestion that they be used as troopships.<ref>Schenk, pp. 340–41</ref> Four [[Coastal trading vessel|coaster]]s were converted to auxiliary [[gunboat]]s by the addition of a single [[15 cm SK L/45|15 cm naval gun]] and another was fitted with two [[10.5 cm SK C/32 naval gun|10.5 cm gun]]s, while a further twenty-seven smaller vessels were converted into light gunboats by attaching a single [[Canon de 75 modèle 1897|ex-French 75 mm field gun]] to an improvised platform; these were expected to provide [[naval gunfire support]] as well as fleet defence against modern British cruisers and destroyers.<ref>Schenk, pp. 129–30</ref>