Operation Sea Lion - German Coastal Guns

German Coastal Guns

With Germany's occupation of the Pas-de-Calais region in Northern France, the possibility of closing the Strait of Dover to Royal Navy warships and merchant convoys by use of land-based heavy artillery became readily apparent, both to the German High Command and to Hitler. Even the Kriegsmarine’s Naval Operations Office deemed this a plausible and desirable goal, especially given the relatively short distance, 34 km (21 mi), between the French and English coasts. Orders were therefore issued to assemble and begin emplacing every Army and Navy heavy artillery piece available along the French coast, primarily at Pas-de-Calais. This work was assigned to Organisation Todt and commenced on 22 July 1940.

By early August, four 28 cm (11 in) traversing turrets were fully operational as were all of the Army’s railway guns. Seven of the railway guns, six 28 cm K5 guns and a single 21 cm (8.3 in) K12 gun with a range of 115 km (71 mi), could only be used against land targets. The remainder, thirteen 28 cm guns and five 24 cm (9.4 in) guns, plus additional motorised batteries comprising twelve 24 cm guns and ten 21 cm guns, could be fired at shipping but were of limited effectiveness due to their slow traverse speed, long loading time and ammunition types.

Better suited for use against naval targets were the four heavy naval batteries installed by mid-September: Friedrich August with three 30.5 cm (12.0 in) guns; Prinz Heinrich with two 28 cm guns; Oldenburg with two 24 cm guns and, largest of all, Siegfried (later renamed Batterie Todt) with a pair of 38 cm (15 in) guns. Fire control for these guns was provided by both spotter aircraft and by DeTeGerät radar sets installed at Blanc Nez and Cap d’Alprech. These units were capable of detecting targets out to a range of 40 km (25 mi), including small British patrol craft inshore of the English coast. Two additional radar sites were added by mid-September: a DeTeGerät at Cap de la Hague and a FernDeTeGerät long-range radar at Cap d’Antifer near Le Havre.

To strengthen German control of the Channel narrows, the Army planned to quickly establish mobile artillery batteries along the English shoreline once a beachhead had been firmly established. Towards that end, 16th Army’s Artillerie Kommand 106 was slated to land with the second wave to provide fire protection for the transport fleet as early as possible. This unit consisted of 24 15 cm (5.9 in) guns and 72 10 cm (3.9 in) guns. About one third of them were to be deployed on English soil by the end of Sea Lion’s first week.

The presence of these batteries was expected to greatly reduce the threat posed by British destroyers and smaller craft along the eastern approaches as the guns would be sited to cover the main transport routes from Dover to Calais and Hastings to Boulogne. They could not entirely protect the western approaches, but a large area of those invasion zones would still be within effective range.

The British military was well aware of the dangers posed by German artillery dominating the Dover Strait and on 4 September 1940 the Chief of Naval Staff issued a memo stating that if the Germans "...could get possession of the Dover defile and capture its gun defences from us, then, holding these points on both sides of the Straits, they would be in a position largely to deny those waters to our naval forces". Should the Dover defile be lost, he concluded, the Royal Navy could do little to interrupt the flow of German supplies and reinforcements across the Channel, at least by day, and he further warned that "...there might really be a chance that they (the Germans) might be able to bring a serious weight of attack to bear on this country". The very next day the Chiefs of Staff, after discussing the importance of the defile, decided to reinforce the Dover coast with more ground troops.