- The Testing Period, January-May 1944
- Schnorchel and the invasion
- Schnorchel and radar
- Schnorchel and radio
1. SummarySchnorchel, an extensible trunk which allowed charging of batteries as well as diesel propulsion and U-boat ventilation while submerged, was first used by U-boats in January 1944. The first few months of use were devoted to experimentation under operational conditions. During the invasion, Schnorchel was used to the limit of its capacity and allowed operation by U-boats against invasion traffic at a time when air coverage was as effective as to necessitate the recall to port of all U-boat's not equipped with Schnorchel. The device was considered of such importance that its installation was designated the chief task of U-boats in port in August 1944. Although Schnorchel was not immune to detection by radar, it was much less susceptible than a surfaced U-boat and permitted boats to operate close to coastal traffic concentrations with little fear of detection for weeks at a time. Unquestionably, Schnorchel was the most effective counter-device developed by the Germans in the Battle of the Atlantic. While a half-way measure in the development of a true underwater boat, Schnorchel did make possible a dangerous approximation of the "Total Underwater Warfare" which the Germans were trying to perfect on blueprints and in the shipbuilding yards.
2. The Testing Period, January-May 1944That the Germans had not devoted all of their time and effort to alleviation of the radiation condition of their search receivers during the latter months of 1943 was clearly shown at the beginning of 1944, when Schnorchel was first used by U-boats operating in the Atlantic Section through various references in radio traffic. The first such reference, in January, gave no indication as to what the device might be, except that it was of a mechanical nature and had some connection with the diesel engines, but the British had seen the term in their reading of Baltic traffic and were able to supply the opinion that it was a cover-name for "an internal combustion system of propulsion which can be used by a submerged U-boat." Later information from traffic, prisoners of war, and captured documents provided extensive knowledge of the device. It was
found to consist of two trunks, one for air intake, the other for diesel exhaust, encased side by side. A valve arrangement prevented entry of water, and an oil pressure system was used to raise the Schnorchel from its horizontal resting position on the deck to its vertical operating position.
The first several months of 1944 were used in gaining information on the performance of Schnorchel in practical use, and Command sent orders at various times requiring U-boat's to make reports on their findings in this regard. In addition, Command was apparently worried over a possible tendency of Schnorchel U-boat's to feel to safe with their new protection, for several times during February and March, warnings were sent that Schnorchel was not secure from location by radar. Replies to requests for information of the practical performance of Schnorchel were evaluated and used as the basis for the Current Order 20, broadcast in 2200 and 2259/31 May, which indicated that several U-boat's had used Schnorchel with success for submerged cruises lasting several days; that charging of batteries could be accomplished by use of Schnorchel for four to five hours daily; that certain U-boat's tended to smoke up during Schnorchel cruising; that Schnorchel could be located by radar only at distances considerably shorter than those at which a surfaced U-boat could be located; and that it was necessary to interrupt schnorcheling approximately every twenty minutes in order to make a hydrophone sweep.
3. Schnorchel and the InvasionThe Allied invasion of France on June 6 brought the Germans not only the opportunity, but also the necessity of using Schnorchel to the limit of its capacity. On June 6 in message 1150, the operational area for Schnorchel U-boat's as previously ordered was changed and they were disposed about the southern coast of England and in the English Channel to interfere as much as possible with passage of traffic between England and France. More than that, within a week, U-boat's in the Bay of Biscay not fitted with Schnorchel were ordered to put into port (2302/12 June), for it had become apparent that the U-boat which was forced to surface in order to charge its batteries in the Biscay area could not survive.
The relative safety of the Schnorchel U-boat, on the other hand, could only lead to the conclusion that boats not already
fitted should receive the equipment as soon as possible; consequently, the summer and early fall of 1944 were devoted with great energy to its installation in the hard-pressed ports of western France. For U-boats which were already fitted, the main activity during the summer was, of course, a concerted attempt to prevent the movement of Allied ships in the Channel area. Fortunately, there was little success in this effort, owing in part, perhaps, to the fact that there was still considerable hesitation in using Schnorchel with the boldness later evidenced by some commanders. Aside from the directly operational objective, boats also concentrated on shortening the time required for charging batteries during Schnorchel operation. The continued confidence of Command in Schnorchel was evidenced in August in an order directing that completion of equipment with Schnorchel should be considered the main task of U-boat's in port, and that boats without Schnorchel should not leave port unless the port was directly threatened (2055/7 Gray).
4. Schnorchel and radarOn the basis of accumulated experiences, message 1333/10 of September 1944, gave an estimate of the effectiveness of Schnorchel as a means of avoiding radar, advising U-boat's that if the Schnorchel was extended only the normal amount, one-half meter above the surface, the impression on a radar receiver would be only about 30 percent that of a fully surfaced U-boat. In addition it was claimed that Schnorchel could not be located accurately enough by radar to permit good placement of bombs. Again the general satisfaction of Command was expressed in an Experience Message in the characteristic style of Admiral Dönitz, signed personally by him (1551/17 October). It stated in part:
the experiences of many commanders have shown that Schnorchel permits cruising without great detours. The Schnorchel allows the U-boat to remain in sea areas close to the coast in spite of very strong patrol and achieve successes there. . . . I require the captains to make the most energetic use possible of the singular capacity offered by Schnorchel and to become master of the enemy defense. Go right to the sources of enemy traffic and attack there . . .
This note of confidence and exhortation was prevalent in communications of Command concerning Schnorchel at the end of 1944, and a new Current Order giving instructions on procedure in operational areas gave considerable attention to the use of Schnorchel in "Total Underwater Warfare." In addition a separate new edition of the old Schnorchel Current Order went into great detail on all aspects of Schnorchel operation. During this period there were scattered references to the apparently satisfactory rubber covering and anti-radar mats with which the Schnorchel had been provided. A final estimate of the value of Schnorchel, for from inaccurate, occurred in a weekly news summary of the German COMINCH (1831/27 January 1945), in which it was stated:
The war at sea has entered a completely new stage through use of the Schnorchel, which makes it possible for U-boat's to remain under water for weeks at a time. The more adroit the U-boat's can become in use of Schnorchel against the enemy, the greater their successes will be.
5. Schnorchel and radioAlong with the decided advantages brought by Schnorchel, the operational U-boat received certain disadvantages quite apart from the question of the crew's comfort during a 70-day submerged cruise. Dampness became a problem, certainly harming the more delicate apparatus aboard. Radio gear was particularly affected. At the same time that the efficiency of standard radio equipment was being reduced, the Schnorchel U-boat was trying to develop the radio communications system of the U-boat of the future, but like Schnorchel itself only a half-way measure was tried. Communications experiments with the Schnorchel round dipole failed to relieve the U-boat from the necessity for surfacing to transmit.
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