Combat experience in 1943 and 1944 had demonstrated beyond doubt that only Type VIIs fitted with snorts could survive against the aircraft and surface ships of the Allied ASW forces. Hence Donitz decreed that all available snort-equipped VIIs should be posted to France (for group Landwirt) and that as many non-snort VIIs as possible should be fitted with snorts in Germany, Norway, and France. However, the intense Allied bombing campaigns against U-boat yards in Germany and the French rail system severely disrupted the production of snorts at the source and the flow of snorts to the U-boat bases in France and Norway.
Partly as a consequence of the Allied bombing campaigns, on D-day, June 6, 1944, only about one-third of the approximately one hundred Type VII U-boat s in Norway and France were equipped with snorts and were combat ready or nearly combat ready: sixteen in France, eight en route from Norway to France, five in southern Norway, and three in Kiel. Nine VIIs were en route from Norway to France to be fitted with snorts at the Atlantic U-boat bases, but, as will be seen, none of these got there. Some authors have greatly exaggerated the threat posed to the Allies by these thirty-two combat-ready or nearly combat-ready snort boats. Therefore the limitations of the snort boats of that era bear repeating.
- Most snorts were technically primitive and newly fitted, and not yet fully debugged. Catastrophic breakdowns in the raising and lowering systems and the exhaust and intake mechanisms were more the rule than the exception.
- Contrary to the general impression, snort boats were not “true submersibles.” They did not snort continuously. Most skippers snorted only about four hours each day, principally to charge the batteries. The rest of the time they cruised at 1 to 3 knots on battery power. Hence the average snort boat en route to and from the operating area could only cover about fifty or sixty miles a day. It took a snort boat nearly three weeks to travel one thousand sea miles.
- A snorting U-boat could not use its radio receivers or hydrophones (passive sonar array), and therefore it was “deaf.” Enemy aircraft employing sonobuoys and surface ships with active sonar (“pinging”) could “hear” a snorting U-boat at a time when the “deaf’ U-boat could not “hear” the enemy.
- A snorting U-boat could rarely use its periscopes. At a snort speed of 5 knots, periscopes tended to vibrate radically, causing the optics to slip out of alignment and, of course, increasing the boat’s visible wake. Except while stopped or making only 1 or 2 knots, a snorting boat was therefore also “blind.”
- Snorts were prone to emit exhaust smoke, visible to the enemy in twilight and daylight.
- Snorts often leaked carbon monoxide into the pressure hull, killing or sickening crewmen.
- When waves dunked the snort, the diesel engines sucked air from inside the pressure hull, causing painful headaches, eye strain, earaches, and other health problems.
- On extended operations, a boat dared not raise its snort merely to ventilate the boat and it had no means of disposing of waste. Hence (as Gunter Hessler wrote), “The atmosphere, which was always pretty foul in a snorkel boat, was further polluted by the stench of decaying waste food and other refuse.” The odor was so repulsive that dockyard workers “recoiled from the open hatch” of a returning snort boat.
- Almost without exception, U-boat crews distrusted snorts and hated to use them.
Inasmuch as the Germans had so few combat-ready snort boats and there were disagreements about where the Allies might attempt to land, it was not possible to position them in advance to meet the Allies head on. Hence, upon orders, the boats would have to sail from Biscay ports to the Allied landing area. To cut the reaction time, eleven of the fourteen combat-ready snort boats of Landwirt were positioned at Brest, the U-boat base closest to the English Channel. However, even by the most direct route (roundabout the island of Ushant), it was at least four hundred miles to the Normandy beaches, a snort trip from Brest of seven or eight days. Once under way, the snort boats would have to deal with Allied amphibious forces protected by heavy ASW forces on extraordinary alert.
Another very serious handicap was the shallow water of the English Channel. Traditionally, of course, submarines shied clear of shallow water inasmuch as it was believed that detection there could be quick and fatal. On the eve of the invasion, however, Donitz attempted to persuade his skippers of the reverse: that operations in shallow waters might be safer. In shallow waters, he said, enemy sonar was apt to be less efficient due to the distortions in active sonar caused by the nearness of the ocean floor and the inflow of fresh water from rivers, which created thermoclines and variable salinity levels, and to the fact that it was difficult for sonar operators to distinguish between U-boats and the many shipwrecks and the metallic debris littering the channel floor. This was not an easy sell, but German submariners could console themselves with the thought that escape and survival from a submarine wrecked in shallow water might be easier. It might also be possible to swim or paddle a dinghy or life raft to a friendly beach.
No matter how one viewed it, the German plan for employing U-boats as the “first line of defense” against Allied invaders was futile. The snort boats might survive; conceivably some might inflict some minor damage. For the non-snorts, operations in the channel would be nearly suicidal.
There were no electro boats available to throw against the Allied invaders. Not surprisingly, the production schedule had slipped badly. The first oceangoing Type XXI, U-2501, was commissioned at Blohm & Voss, Hamburg, on June 27; the first small “duck” Type XXIII, U-2321, at Deutsche Werft, Hamburg, on June 12. The OKM diarist logged on July 30 that “six” Type XXIs had been “delivered” (i.e., commissioned) and that it was hoped a total of 144 would be delivered by the end of 1944. It was also noted that the expected delivery of Type XXIIIs by October 1 had been reduced from forty-three to twenty-three boats and that, owing in part to the loss of eighteen boats under construction in Genoa, it would not be possible to complete eighty-seven Type XXIIIs by the end of 1944.
Delays continued to mount. Actual deliveries of electro boats by the end of 1944: sixty-one Type XXls and thirty-one Type XXIIIs, all with flaws, none combat ready.
