We are glad to present copy of a memorandum probably written by Admiral Legnani or by members of his staff . This document was located by Dr. Achille Rastelli in the archives of USMM (Ufficio Storico marina Militare) in Rome.
CRITICAL EXAMINATION OF OUR READINESS AND RESULTS
OF OUR SUBMARINE WARFARE
(Until early December, 1941)
In this memorandum are examined in order:
A. The experience acquired by the German, British and Italian Navies in the field of antisubmarine warfare by submarines in the First World War and the lessons each navy might have learned.
B. The deficiencies of our submarine fleet in comparison to the German one, both in regards to equipment and personnel, and the measures implemented to improve the situation.
C. The nature and volume of the British antisubmarine activities and the repercussions [it has had] on the utilization, successes, and losses of our submarines.
D. The fundamental influence exerted by the lack of aerial collaboration on the Italian side, and by the extensive British aerial antisubmarine activity.
For a critical examination of the development of the underwater warfare which has been and is [currently] being fought in the current conflict, it is necessary to look back
at the events and experience of the [First] World War and take into consideration at least three Navies: German, British and Italian.
I THE GERMAN NAVY
The German Navy has come out of the World War with expertise in the use and understanding of the offensive capabilities offered by submarines so vast and profound and so superior to the one collected by other nations making the Germans, even after the war, the only power which has been really capable of taking advantage in this field of the lessons of the Great War.
This can be easily understood if one realizes that Germany during the Great War built at least 344 submarines which, in thousands of war missions, have sunk nine millions tons of enemy shipping. All the nations of the Entend had at the most 100 submarines, and they achieved negligible results due to lack of targets.
The peace terms imposed upon Germany forbade it to build submarines, but they could not take away the precious experience acquired, nor could they impede it from taking advantage of the research and improvements of prototypes (to be mass produced in case of war). Also, the Germans could not be stopped from continuing the study of the best methodologies, and the preparation of the best instrumentation and material adept to solving all the problems which the future war might bring forward.
The capabilities and excellence of the German industry took care of the rest.
In summary, the link between the two wars could be described as follows:
In 1918 Germany had a submarine fleet far superior in quality (and also in quantity) to those of any other power. Nevertheless, the a.s. mobilization of the Entent caused the submarine campaign to decline, and the German submarines began becoming obsolete.
Between the two wars, Germany dedicated itself to the research and construction of new characteristics and new uses capable of giving back to the submarine units the offensive aptitudes which had been mostly lost. This way, the German submarines made a new leap forward (naturally unknown outside Germany) toward progress.
Thus, Germany reached the new war in conditions somewhat similar to those it had at the beginning of the previous war: a relatively small number of boats (about fifty), but rapidly increasable, and with unknown characteristics, but surely superior to those of all other navies, thus creating a real surprise to the enemy.
This way, the balance between offensive and defensive naval means, which had broken in 1914 and which was gradually reestablished between 1914 and 1918, was again broken in 1939. It could be assumed that this may again be established during the war.
II The British Navy
The British Navy, on the contrary, left the previous war
with a mature and glorious experience in antisubmarine warfare, to which the other navies of the entente also contributed, but undoubtedly in a comparatively very modest proportion.
The British navy was therefore, since 1918, the only navy which had collected the full experience in the area of antisubmarine defense, research, and antisubmarine warfare (active, passive).
Furthermore, Great Britain had the economic and industrial capabilities to take advantage of this precious experience. Therefore, in the interval between the two wars Great Britain did not crystallize the means and methodologies to her disposal in 1918. To the contrary, the Royal Navy, has depended on and perfectioned for 20 years with generous means and clear vision the complex problem of AS warfare. Thus, it has reached in this field a high degree of perfection, the highest obtainable in relation to today’s technological progress.
Considering also that Germany was not allowed to build submarines, but that other navies were doing so in large numbers, it should be understood that Germany would have not remained completely still and could have made further progress (to which the Royal Navy would have probably not arrived since it dedicated limited attention and resources to submarine warfare).
III The Italian Navy
The Italian Navy, different from both the German and British ones, did not harvest in the Great War experience in submarine and antisubmarine warfare which could be used as a base for a war in the Mediterranean and in the oceans.
To understand this inferiority in respect to the German submarines, one should only consider that while at the beginning of 1915 the German submarines were capable of missions lasting several weeks and were capable or transferring non-stop from the North Sea to the Adriatic (3000 miles), in 1917 the Regia Marina was conducting the war still using small F class submarines capable of missions of two or three days only crossing the Adriatic (50 miles)!
Therefore, to be perfectly up to par with the hard and enormous assignments of a naval war against Great Britain in both the Mediterranean and the oceans, between the two wars the Italian Navy should have been able not only to overcome the gap with the German and British navies, but also keep up with their progress. All this should have been accomplished based on someone else’s experience, which is never well known, as convincing and as instructive as one’s own. Taking advantage of a domestic industry more or less up to date and powerful, figuring out and understanding the improvements and progress of the other navies which kept their secrets jealously. (The technical collaboration with the allied Navy had the first results only when our submarine fleet was in grand part
already built, and had already entered the construction phase following the beginning of the wa).
Under these circumstances, the Italian navy had made great progress, but not the much greater one which would have been necessary and started the war with a submarine fleet which could have been very powerful and to be feared under the conditions of the previous war, but resulted in low efficiency under the new conditions of the aero-naval war.
Some of the most visible deficiencies of our submarines had been brought to the surface during the Spanish War. This preceded by only three years our intervention in the current conflict, and anyway the experience in Spain cannot be compared with that of a large aero-naval war against Great Britain, just as the campaign against Ethiopia could not clearly constitute a comprehensive experience of land conflict against a European army.
The real comparison with the more advanced submarine units in the world has therefore taken place only during this conflict through the first contacts between our forces deployed in the Atlantic and the German U-Boot. And the real comparison with a more advanced AS organization could be determined only following the clash with the British naval power.
These comparisons have demonstrated that the gap which separated us from the German and British navies had not been sufficiently reduced.
The demonstration took place through the limited successes (obtained) and the gravity of the losses. Or better by examining “the quantity of the results obtained and the losses suffered”.
It should be noted that German losses were also very hig;, the difference is therefore in the amount of results obtained, not to mention the much larger German ability to replace units lost.
In the following part of this memo we shall examine in great detail the reasons for the serious losses and the poor results.
B- COMPARISON BETWEEN THE ITALIAN AND GERMAN SUBMARINES – IMPROVEMENTS AND MODIFICATIONS [MADE] TO THE FIRST ONES.
Although the poor results and the high losses are in evident and clear relation, the need for an analytical exposition [of the facts] dictates and artificial distinction between two the topics. This suggests faulting the deficiencies of our boats with the poor results, and [credit] the high losses to the efficiency of the British countermeasures.
After all, this conceptual distinction is quite faithfully reflected by geographical separation. In the Atlantic war, where our submarines found themselves in comparison with the German units, it has been quite obviously revealed the inferiority of their characteristics which translate in a lesser yielding in the fight against enemy merchant traffic. Instead in the Mediterranean war, where the enemy traffic was scarce, and for these reason
more difficult, the gravity of the losses has particularly highlighted the efficiency and intensity of the countermeasures practices by the enemy.
In comparison with the German units, the Italian have shown the following deficiencies or technical inferiorities:
I. Lower surface speed, and a lesser aptitude to maintaining normal speed in adverse weather conditions, and a less secure operation of the engines. This deficiency makes the reaching or passing (to then attack) of units or convoy impossible, which are instead accessible to attack by German units.
II. Better visibility
The superstructures are more extended, and the outer casing (in surface navigation) is more exposed. Thus our units have a lesser probability of success or a greater risk in night deployments.
III. Greater noise
The machinery for surface navigation and especially those indispensable for submerged navigation, or to level the submarine at a given depth, resulted very noisy compared to the German systems, with serious consequences in regards to detection by the enemy’s hydrophones [systems].
IV. Higher diving time
The diving maneuver (which in the various submarines in service ranged from 60 to 120 seconds, with some even
exceeding the latter value)resulted being double and four folds of that of the German submarines. Thus derives a much greater vulnerability to daylight aerial attacks and to the reaction of surface units during night actions.
V. Lesser maneuverability
In general, Italian units have turned out to be less handy and maneuverable than the German ones. For example, the surface turning radius for the German units is reduced to only 300 meters, thanks to the installation of a double rudder, where it is about 500 meters on our units.
VI. Inferiority of the weapons and instrumentation for their deployment.
A complex problem relative to the stealthyness of our submarines, effectiveness of their weapons, and their rational and profitable, use resulted to be already resolved and implemented aboard German units, while these issues are still under study and experimentation within the Italian navy. Thus, to limit ourselves to the main questions, it should be noted that German submarines are equipped with:
1) Torpedo launchers which do not generate an air bubble revealing the position of the submarine upon the launch of the torpedo.
2) Electric torpedoes which do not produce a tail and thus do not allow the target to maneuver avoiding the attack, and the enemy light unit to move toward the origin of the tail to search and attack
the attacking submarine
3) Fire control and launch systems capable of simplifying, automating, and preventing computation errors, and communication relative to the preparation and execution of the launch, both on the surface and under water.
4) Torpedoes with magnetic pistols which have revolutionized naval technique for various reasons, but remarkably because they have a conflagration effectiveness greatly superior, and cause damage to the lower part of the hull which is not provided with any protection (our submarines on the contrary, if they do not want to take the risk to let the torpedo pass below the target without striking it and exploding, are forced to set the run for lower depth, thus hitting the hull on the side where it is better protected. This causes an explosion path which is partially let out into the air outside the target obtaining much lesser destructive power).
Beside the magnetic pistols, and the fundamental advantages they offer, our torpedoes have shown poor effectiveness during conflagration due to the incomplete burning of the explosive and the deformation of the warhead during the explosion, and for other reasons which have induced [us] to begin again the study of the behaviors of these weapons to modify and improve them.
This could explain why the damages inflicted on the
enemy units have been generally light, to a point that British warship torpedoed by our submarines have almost always been able to return to base and not too rarely we have had no news of long immobilization of the stricken units due to repair work.
It should be kept into consideration that the British units have generally shown considerable structural strength and excellent damage control. Furthermore, the evident statistical documentation of the little results obtained even in those cases in which the submarines were able to launch is contained in addendum I (torpedoing carried out by submarines from the beginning of the war until December 9th, 1941) – without the result of the action becoming apparent.
VII Inferiority of the equipment and outfitting in general.
All the equipment and its general arrangement aboard German submarines have shown to be clearly superior to that of our units under all aspect:
1) Strength and safety of operation.
Our units have had much more frequent failures which, not only have reduced the percentage of submarines on patrol, but at times have placed the submarines in precarious circumstances while facing the enemy. Undoubtedly, these deficiencies have reduced the absolute trust of our submariners in their weapon, condition this indispensable for maximum success.
[it has also] forced our crew to [perform] arduous repairs during patrol (and even in the period following their return to port from a patrol when they instead should have been resting, but had to [work] due to the deficiencies of the overhauling equipment at the bases).
2) For simplicity of operation or perfect adaptability of the material to the task, deriving from a long and meticulous experience and non-stop studing of even newer improvements.
It is obvious that a single cause of inferiority could by itself be very serious, while the concurrency of all of the factors [cited], and [those also] omitted for the sake of brevity, becomes extremely serious.
Thus defining as 1 the war performance of a German submarine, and estimating only slightly lower the one of an Italian submarine – for instance 0.8 – the performance of an Italian submarine due to the combination of the seven more complex causes of inferiority which have been [previously] listed (if all of the causes are globally considered) reduces the performance to .8 to the 7 factor, or .21.
This calculation, which serves as guidance, refers more than anything else to the chance one of our submarines has to perform its duties to the end: bring the torpedo to explode upon contact with the enemy hull. But if the weapon is instead, due to built-in defects, incapable of sinking or even seriously damaging the target, then due to this main deficiency, there is no longer any ratio which is worth computing. This one [deficiency] alone is enough to destroy the fruits of all labor, all fervor, and sacrifices of the entire submarine fleet.
The realization of the inferiority of our underwater units, and the examination of the measures adopted in the German constructions, did not allow to immediately begin the alteration and improvements which would have been desirable to do.
In fact, it was necessary to study if and what building criterion could be applied to our units, and which particular device [to improve], since it was not a new construction or a new project, but units already in service. It was necessary to prepare the material required and, if necessary, conduct testing, deepen the [understanding] of specific issues and ask for the consultation [services] or production [facilities] of the Germans, whenever it was not possible provide to with domestic means.
In the meantime, it was necessary to keep on fighting
the war, continuing to employ our submarines as they were, delaying each [boat] alteration to [when] longer periods of maintenance or repairs [were due].
Amongst these difficulties, which applied to all kind of units, it was added one specific to submarines. This was of such a nature and gravity to complicate any issue and augment any preexisting difficulty. As a matter of fact, the sine qua non condition for the submarine to operate is that with the double tanks flooded its weight be equal to its buoyancy and it position of balance leveled [bubble]. Thus, differently from any other kind of ship, any alteration is restricted to the requirement that the total weight of the ship be kept the same, and the new distribution of weight be such not to cause any variation of the longitudinal trim.
Despite all these difficulties, and in particular this double restriction, numerous and important alterations were made or are being made to the submarines.
Amongst them, it is worth mentioning (see addendum 2):
1- Reduction of the size of the conning tower to make the submarine less visible
2- Increase of the size of the crash dive tank, and other changes meant to increase diving performances.
3- Replacement of the Rovereto stabilizer – noisy and usable only up to 90 meters – with other systems, quieter and usable
at all depths, and better suited for trimming the submarine while still and submerged.
4- Adoption of gimbals [dampers] for noisy machinery to elude enemy hydrophone searches.
It is understood though that only aboard units of new construction, and particularly those designed when the new war experience had already matured, it was possible to implement improvements in all essential characteristics, including surface speed.
All this concerns the equipment. The realization of its inferiority has not however diminished the officers’ and crews’ very aggressive spirit. Nevertheless, the deficiencies detected in the first months of war are not limited to the equipment.
Since the beginning of [our] participation to the Atlantic campaign, it has been evidenced that aboard German submarines great part of the crew (officers, non-commissioned officers, and crews) were in grand part much younger than our personnel, thus much more resilient to the hardship of life aboard submarine units. Meantime, is has been shown in the Mediterranean, as well as in the Atlantic, that our submarine personnel, older and better experienced, did not last under prolonged combat life. In short, it has been necessary to disembark the almost complete role of the most expert captains and the most skilled non-commissioned officers.
Thus was lost a precious accumulation of experience collected over many years of training, and it was necessary to quickly make room for the younger ones. But for those, experience could not be improvised.
The “Submarine School” was immediately established, and at the moment it has began giving results in the form of a noticeable outpour of trained young personnel; but this is yet to equal demand. In any case, the institution of [the school] has not been able to avoid a shortage of personnel, which has not yet been overcome.
C – BRITISH ANTISUBMARINE ACTIVITIES AND LOSSES OF ITALIAN SUBMARINES
We now move to cover the British A.S. activities and the consequences it has had on our submarine warfare. It behooves us to state that the efficiency of the enemy’s A.S. organization, and its equipment and techniques constituted unknown factors (as for all other matters regarding readiness of the enemy, especially at the beginning of the war).
Nevertheless, according to public statements, the British and French fleets were equipped with ultrasound search apparatuses capable of localizing a submerged submarine with accuracy, even if perfectly silent. The principle used by this echo-sound equipment was well known in Italy and doubts were solely concentrated on the practical construction of [a devise] with a sure range of a few kilometers.
It is understood that a device capable of locating or detecting with absolute certainty, and capable of estimating range of a submarine underwater would have devalued the underwater weapon and would have made a submerged submarine blind, slow, without defense, and an easy prey to the enemy’s surface fleet.
Under these circumstances, it was clear that the submarine could have not conducted its activity whereas it would have been completely abandoned to itself in face of all the enemy’s offensive means (has it has happened in the past war). [The submarine] would have necessitated support activities by our surface ships, especially our airplanes, to counteract the offensive activity of the enemy’s ships and airplanes.
Practically, the enemy search equipment demonstrated characteristics as to make impossible for a submarine to attack making its loss sure, only if it had encroached within the range of a few kilometers of the enemy’s torpedo boats. Nevertheless, it has made more difficult to conduct an attack to the end, and less easy to avoid the reaction of the enemy.
What was specifically said in regards to the equipment for the search of the submarine underwater should have also applied in general terms to the whole British A.S. organization, both in regards to quality and quantity of their means.
Basically, this British organization has demonstrated to be equal to its role and could be summed up into two [items].
– Defense: prevent or impede attacks by our submarines against their war and cargo ships.
– Offense: conduct the search and systematic hunt of the enemy submarine carrying on to its destruction.
Naturally, offensive results could be obtained much more easily when longer, more intense, and undisrupted could the activity of the British A.S. vessels be. This [would take place] preferably near British naval bases, thus patrol areas which could have yielded the best results, both in terms of exploration and attack, have to all practical matters caused the greater losses without [producing any] results and have shown to be unsustainable.
Clearly, as the submarine move further away from the enemy bases, the probability of finding good targets diminishes. On the other hand, the enemy A.S. activity should have also decreased and this should have allowed a compromise solution in the selection of the geographical distribution of the patrol areas to balance the two needs; bring the submarine closer to the enemy bases to bring them for sure on the target’s routes; move further away from the enemy bases to spare them from an un-contrasted and perennial hunt and its consequences.
Thus the British naval and aerial dominance was full and unchallenged in very large areas of the Mediterranean. Sometimes, the aerial and naval defenses lacked even in the proximity of our submarine bases. This, in various circumstances, has allowed the enemy destroyers and airplanes to chase and attack Italian submarines up to the landing channels leading to our ports. [For instance] it has happened during the first months of the war to the submarines assigned to the base of Tobruk; more than one of them has been hunted and sunk by the enemy a few miles from their logistical base.
Beside the action and counteraction extraneous to the submarine fleet, we were left only with using submarines with limitations and difficulties set forth by the above-mentioned situation. The experience of this hardship and limited possibility of use has matured thorough the [experience acquired during the] war fought and the losses suffered.
Evidently, the units which could have provided for the most precise information about the means and methods of the British A.S. effort where precisely the ones which did not return to base (it could be of interest remembering that during the last war the Germans did not have knowledge of the existence of the British Q ships which had already made various kills until the day one of their submarines was able, by miracle, to elude the fire of one of these special and ingenious units.)
Nevertheless, the nature and efficiency of the enemy A.S. was quickly understood since the first weeks of the war; new orders were immediately issued to adapt the use of the submarine to the real conditions in which they had to operate.
However, due to further and continuous reevaluation of the operational guidelines of our submarine units, and the orders thus were issued [in response] to the incessant search for the best solution between the two opposing compromising needs: reduce the losses to tolerable levels; do not reduce to unacceptable level the probability to meet, discover and attack the enemy and sink it. This problem in additional to the already mentioned problems of the geographical distribution of the patrol areas we were presented with the selection of modality and most of all the depth of the attack.
Low depth patrols (which allow for the use of the periscope and which was the method used in the past) in addition to causing grave losses, has generated minimal results because the submarines are easily detected.
On the other hands, at greater depth and with the [aid] of the hydrophones, it has proven at the most capable of avoiding being located, but not suitable for the timely detection of the enemy units to be attacked.
The daylight use, going back and forth between these two methods, could be in general assessed as a complete failure, especially in the Mediterranean where the targets are very limited in number
are made up mostly of warships or convoys escorted by a large lumber of aircraft and ships.
Some success with fewer losses was instead obtained during night surface operations, but naturally this kind of use has a much lower yielding because of the limited range (thus low probability) of sighting enemy units.
D- THE ROLE OF THE AIRCRAFT IN THE ITALIAN SUBMARINE WARFARE AND IN THE BRITISH ANTISUBMARINE ACTIVITY
In addition to what has already been presented, it is understood that there are two primary reasons for the poor performances of our submarine warfare: on one hand, the high efficiency of the British aero-naval collaboration in fighting submarines; on the other hand, the complete absence of collaboration of the Italian Air Force in support of the [Italian] submarines.
These two factors, considering their fundamental importance, deserve a dedicated examination, although a generic and schematic one.
On the side of the British exists an air force which is an integral part of the fleet, thus it could be organized, trained, and could operate in perfect harmony with the surface ships commencing before the war and with absolute strategic unity.
Consequentially, in addition to the British naval control of vast parts of the Mediterranean, there was also an unchallenged aerial domination. It is mostly due to this latter [factor] if our submarines have been easily located, monitored,
and attacked during daylight surface transfers and periscope patrols, and their presence communicated to the surface ships.
Thus, large enemy ships have been able to avoid them, while smaller units have sought them out and attacked them.
To avoid being sighted from the sky, since this made them unable to attack, our submarines have been forced to limit their stay on the surface and at periscope depth with the repercussions, as already said, on their ability to attack.
On the Italian side instead, the hierarchic separation at the technical and organizational level between ships and airplanes in preparation for the war has constituted a serious obstacle to clear collaboration within their tasks. Even under the urgent needs of the current conflict, it has been impossible, despite improvisation, to overcome this problem.
Thus, our few airplanes, not previously trained for operating at sea, and also employed with methods and goals independent from submarines warfare and operated by commands linked but separate, have contributed only minimally to providing information for both offensive and defensive [operations]. Instead, such [collaboration] has been formidable for the British submarines. Thus without considering the number of airplanes available, the Italian air force has fought a parallel, but separate war.
1st) The German submarines have obtained great results against Great Britain despite the high efficiency of the British antisubmarine defenses because they have special and excellent characteristics which make them far superior to all other [submarines], and in particular to the Italian and British ones.
2nd) The Italian submarines have achieved limited successes against Great Britain because of inferior [technical] characteristic than the German ones and because opposed by an excellent antisubmarine organization.
3rd) The British submarines have achieved considerable success against Italy even though they are similar to the Italian [boats] and inferior to the German ones because opposed by a poor antisubmarine organization.
4th) The airplane has played a fundamental influence on these results – positive or negative – and in general on the whole progression of the offensive and defensive submarine warfare of the German, British, and Italian navy.
As expected, war and its results have highlighted:
a) The large participation and collaboration of the German airplanes and submarines against British traffic.
b) The large participation and collaboration of the British airplanes and submarines against Italian traffic and the extremely effective
collaboration between naval and air forces in antisubmarine activity against Italian submarines.
c) The almost absolute absence of aerial collaboration in the deployment of the Italian submarines and in seeking, signaling, and attacking British submarines.
In regards to the real deficiencies of the submarine fleet, measures have been taken and we are still working on eliminating them on units already in service or under construction, and within the limits allowed by each of them and the resources of the nation.
From this action we could expect a better, but not complete change of the situation, because in the meantime it is to be expected that the German submarines would continue improving and the British submarine organization sharpens and increases in power.
In any case, future results will remain strictly linked to the nature and magnitude of the changes implemented assuming a more efficient and direct participation of the Italian Air Force in submarine warfare.
Translated by Cristiano D’Adamo