ABSTRACT

The German Naval High Command became increasingly aware that despite the growing numbers of the U-boat fleet, individual U-boats were sinking progressively fewer ships. Moreover, the enemy were growing ever more concerned at the delays to U-boat transits caused by Allied air power in the Bay of Biscay and, towards the end of 1942, they began feverishly searching for ways to redress the situation. One solution was to adapt their existing U-boats by fitting an extendable air intake, known as the ‘schnorkel’ (literally a ‘nose’), which allowed them to draw air into the boat while submerged at periscope depth. This made it possible for the U-boat to propel itself on diesel engines without depleting the battery charge, and simultaneously to refresh the boat’s air. It was assessed by the Admiralty that this system could be used in sea states up to 3-4 and that the schnorkel head would present only a small target that would be extremely difficult to detect by radar (or by eye) and would make the U-boat practically invulnerable to air attack.1 Even with the urgency needed by Allied pressure, the Germans had only begun sporadic development of the schnorkel. By late 1942, U-448, while working-up in the Baltic, was fitted with an H-shaped, experimental type and, although the equipment achieved moderate success, it was removed and further sea trials temporarily abandoned. Nevertheless, by December 1943 an improved design was being fitted to operational U-boats at St. Nazaire, with the first Baltic boats equipped and an instructional programme started in the following February. The enemy’s priority was fitting U-boats in the Biscay ports as a means of safely transiting the Bay en route to their Atlantic operational areas. Only later did the Germans realize that schnorkel boats would have an advantage in operations against an invasion of the Continent. The last boats to be fitted were those based in Norway, the first of which only appeared in early September 1944 (though not all Biscay boats had been fitted by that date). British interrogation of prisoners-of-war (PoW) revealed that by mid-August 1944 about one third of the Type VIIs and most of the Type IXs had been fitted.2