AT THE END OF HOSTILITIES, the Director of Operational Research in the Admiralty undertook to analyse all the torpedo attacks made during the war by British submarines and Allied submarines under British operational control. The information was extracted from submarine patrol reports and entered on punched cards for use in a Hollerith machine, which was a simple mechanical computer. The results were issued in a series of short reports during 1950, and were graded 'Confidential' with a somewhat limited distribution among interested Admiralty departments and establishments. Few wartime submarine Commanding Officers saw these reports, and one that did remarked facetiously that it only revealed two things; firstly that submarine captains with red hair were the most successful and secondly that it was easier to hit with torpedoes when you were closer. The report became available for all to study in the Public Record Office in 1981, after the statutory thirty years. It is true that there were no startling revelations in the report, and that most of the investigation confirmed what had been well known throughout the war. Nevertheless the mass of figures and tables are of extreme interest and are a valuable contribution to naval history. The Hollerith analysis, however, was not complete. It only used the data over the years 1941- 1945. Presumably this was because it was found that the records for 1939 and 1940 were unsatisfactory in some way or could not be found. The result is that the totals are incorrect for the whole war. For instance the number of torpedo attacks is given as 1732, but this is only for 1941 to 1945, and the total for the whole war was 1893. There is, however, no reason to doubt the validity of the conclusions, especially when expressed in percentages.

The report identifies 7640 contacts made by submarines when on patrol. Some 4522 of these contacts were made from submerged through the periscope and so in daylight. Another 2585 were made on the surface by visual sighting from the bridge. Some of these were made by day, but the majority were made using binoculars at night. First contact was made by listening on asdic for enemy propeller noises in 410 cases, 56 when the submarine was on the surface and the rest when submerged, generally when at periscope depth. First contact was made by radar when on the surface in only 46 cases. The visual range of contact both from the bridge and by periscope was often, of course, limited by poor visibility, but could be as much as twelve miles. At night, sightings by binoculars were normally in the 3-5 mile bracket, while when submerged by day using the periscope they were greater, generally in the 5-8 mile bracket. The range of contact by listening on asdic varied widely with the noise made by the target; the sea conditions and geographical area and also whether the submarine was on the surface or submerged; not to mention the class of submarine and type of asdic set. A large ship proceeding at speed in good asdic conditions in the Mediterranean could often be heard by a U-class submarine, even on the surface, at twelve miles. The same target at the same speed off the Norwegian coast in a gale would be unlikely to be heard before it was sighted. The average range of contact of a ship was probably 2-5 miles whereas a submerged U-boat would probably not be heard at all. The 46 first contacts by radar, seems to us today, to be very small. Radar, however, was not fitted in submarines until the end of 1941 and was not universal until well into 1943. The type 291 set, although designed for use against ships as well as aircraft, seldom detected ships at over five miles. It was not used at night by many Commanding Officers for fear that it would be picked up by enemy search receivers and give the submarine's position away. Anti-shipping radar sets that could not be detected by the enemy were not fitted until the very end of the war².

Of the above 7640 contacts, 1732 developed into attacks in which torpedoes were fired, and the report is at pains to investigate why the remaining 5808 contacts were not attacked. By far the largest category, of 2726 contacts is one in which the patrol report gives no reason, almost certainly because it was too obvious to the submarine commanding officer to need comment. Most of these contacts were probably fishing craft, minor patrols or other small vessels. The second largest category of 848 contacts is a curious one. It is said to include all those cases were fire was withheld because 'the risk was too great'. Undoubtedly there were some such cases, but the number seems very high³. This category must, I think, refer mainly to the sighting of major patrol vessels such as destroyers, torpedo boats and corvettes, which it was the policy to evade in the hope of being subsequently able to attack more important targets. The reasons given in the patrol reports that many other targets were not attacked were more specific. No less than 568 passed out of range and 387 could not be attacked because of attack restrictions in force. Another 259 were clearly engaged in anti-submarine operations and were evaded; 257 were obviously unsuitable targets for torpedoes, being too small or of very shallow draught. Finally 48 were not attacked because of a shortage of torpedoes and 39 were identified as neutral vessels.

The next point to be addressed was the use of elderly torpedoes fired during the shortages mostly in 1941. Five salvoes of Mark II torpedoes were fired, and these torpedoes were manufactured during the First World War and so were over twenty years old. They had already been reduced to the status of 'special fleet practice' torpedoes before the war and were being expended to hit during exercises. Enough warheads were, however, found for some 21 of them to be used in action during the torpedo famine of 1941. Exactly one hundred salvoes of Mark IV torpedoes, 281 in all, were also used in action and these torpedoes, although of First World War design, were younger and still in service as the action outfits of the older submarines. All of the remaining 1475 salvoes were of the modern Mark VIII torpedoes. The analysis did not show that the older torpedoes had a high failure rate or could be blamed as the cause of misses any more than the modern torpedoes.

The investigation then turned its attention to other reasons but in nearly a third of the attacks, 319 out of 1044, no obvious cause could be deduced. No doubt in these cases the cumulative effect of a number of errors caused the torpedoes to miss, or else there was a reason which was not apparent at the time and which has not come to light since. No less than 193 misses are attributed to the firing of too few torpedoes in a salvo. This was especially so early in the war. In 1941, 63 misses were attributed to this cause whereas there were only six of these misses in 1945. The high figure for 1941 was certainly partly due to the shortage of torpedoes and a desire to economise, but a failure to study the subject in pre-war exercises can also be blamed.

The next reason for missing was assessed as 'bad conditions' and 142 cases were identified. 'Bad conditions' covered poor visibility due to fog, rain, snow or haze as well as sea conditions, which, in a gale, could be sufficiently adverse to make depth keeping of the submarine and periscope watch very difficult. It also made the proper running of the torpedoes doubtful. To quote the report 'the chance of success was sometimes highest when smooth or slight seas prevailed, and at other times when moderately rough seas obtained, but never when the waters were flat calm'. A flat calm made it easy for the enemy to see torpedo tracks and periscopes and enabled aircraft, especially in the Mediterranean, to see the submarine submerged.

The next largest group causing misses was the failure of material and this category added up to 107 cases. By far the most likely torpedo defect was a gyro failure: there were 94 of them, which would cause the torpedo to run crooked or to circle. There were 28 torpedo tube misfires, and another six in which there was a delay in firing. In 23 cases, torpedoes exploded prematurely, generally short of the target. There were two cases of torpedoes counter-mining other torpedoes of the salvo, and thirteen where the torpedoes failed to explode. Most of these were when using the CCR pistol. Thirteen torpedoes failed to run altogether and eleven hit the bottom on discharge. There were also another 37 failures due to miscellaneous causes including breaking surface and 'nosing'. Listing these defects creates a bad image for our torpedoes, but it must be emphasised that in 1505 salvoes, all the torpedoes ran correctly and the 107 defects represent only 2.17% of the torpedoes fired, which was better than in pre-war practice firings.

The next group of failed attacks were when torpedoes should have hit but ran under the target. There were 87 of these and the reason was generally the shallow draught of the target. It could also have been due to the torpedo running deeper than set. The minimum depth setting for the Mark VIII torpedo was eight feet and small ships, especially when in ballast, might well have a shallower draught than this. Torpedoes took a few hundred yards to steady at the depth set and, if fired at close range, could also run under. Another cause of attacks failing was that the enemy sighted the tracks and took avoiding action. This happened in 67 attacks, which might otherwise have proved successful. It was more likely to happen by day when the sea was slight or calm. The final group of missed attacks were those due to errors of estimation of the target's course and speed, or of the size of the target by the Commanding Officer, or else of drill or control errors by his crew. There were 82 cases of errors of estimation to which the failure of the attack can be attributed, the enemy speed being the most usual, and 47 failures in drill or control procedure.

We now come to the important subject of the effect of range on the success of submarine attacks. Was it, as our facetious friend, referred to earlier, suggests, easier to hit when you were closer? The table below, however, which has been constructed from the information supplied in the report, shows that the problem was slightly more complex.

Table showing number of submarine attacks made in 1941-45 and their success rate according to range

Range in Yards No of Attacks Hits Misses % of Hits

0-1000 301 124 177 41% 1000-2000 505 235 270 46% 2000-3000 301 133 168 44% 3000-4000 234 77 157 33% 4000-5000 138 46 92 33% 5000-6000 100 33 67 33% 6000-7000 59 18 41 30% 7000-8000 37 8 29 22% over 8000 26 6 20 23% Not known 31 8 23 25% 1732 688 1044 39%

The Naval Staff in the Admiralty were, at the time of the circulation of the Hollerith report, particularly interested in finding the optimum size of convoy. They therefore requested more information on this subject. Many figures and tables were produced, especially to discover whether convoys were detected at a greater range than independents. Little came of the investigation, however, mainly because the convoys attacked by our submarines were so small. Half of the so-called convoys attacked, consisted of only one escorted ship and there were seldom more than four escorted ships. The operations of our submarines were therefore very different from those of the U-boats in the Battle of the Atlantic. Flag Officer(Submarines) was interested in whether stern torpedo tubes should be fitted in future submarines, and was intrigued by the fact that stern torpedo tube attacks, although few in number, had a higher success rate than bow torpedo tube attacks. The reason for this seems to have been that stern tubes were normally used only when the bow tubes could not be brought to bear, and this was generally in short range attacks. The only occasions on which stern tube attacks were made deliberately were when all the bow torpedoes had been expended.

The Hollerith investigation also looked into the effect of age of the Submarine Commanding Officer and his experience in command in war on his success rate. The tables show that the age of submarine commanding officers decreased rather than increased during the war. No clear trends could be found in the tables. Commanding Officers in their mid twenties did well, and in the later years of the war, those over twenty-eight did better. The success of commanding officers on their first few patrols was found to be 'impressive' but those with plenty of experience were better still. In general, age and experience did not seem to be important factors in success. Some submarine commanding officers, whatever their age or experience, were simply shown to be better than others.

In 1946, before the Hollerith investigation was begun, Lieutenant Commander LW Napier, an experienced wartime submarine commanding officer, had been attached to the staff of the FOSM to investigate salvo firing from submarines during the war. This investigation was to include the number of torpedoes fired in an attack, the spread of the salvo and the point of aim. His figures were later checked and put through the Hollerith machine and attached to its report. They produced probably the most useful facts to emerge from it. Lieutenant Commander Napier's first finding was that, consistently throughout the war, too few torpedoes were used in a salvo. Too many torpedoes were seldom fired, but when they were, they produced a higher hitting rate still. In 1941-2, there was good reason for economy as torpedoes were in short supply. Throughout the war, however, there was a tendency to conserve torpedoes, so as not to run out of them altogether when on patrol. During 1943, for example, 56% of salvoes, which used the right number of torpedoes, obtained a hit, while only 34% hit when too few torpedoes were fired but 71% obtained a hit when too many torpedoes were expended. In general, the spread of a salvo gave the best results when calculated correctly, for instance in 1943, it showed 46% hits while it was 39% when the spread was too great, and 21% when it was too small. A common fault with the point of aim was to be too far ahead, but when it was too far astern it often produced better results. This was probably because it gave a greater chance against ships that took avoiding action. The Napier analysis, confirmed by the Hollerith investigation, therefore drew attention not only to the errors in firing salvoes but also to the method of firing the salvo itself. The 'hose-pipe' salvo used with a firing interval meant that when there was an error in estimating the enemy speed, and so in the calculation of the director angle, there was also an error in the spread of the salvo. The individual aiming of each torpedo overcame this difficulty but a 'hose-pipe' salvo was easy to avoid. If the first torpedo track was sighted and avoided, then automatically all the other torpedoes were also avoided. A system of spreading by gyro angle would have overcome these difficulties to a greater extent. There is little doubt that the method and training in the firing of torpedo salvoes by British submarines was a major reason, if not the major reason, for missing the target. Much work to try to improve matters was put into the subject by mathematically minded submarine captains during the war, but the staff of the FOSM and the Admiralty departments responsible did little to improve matters, or even to identify what was wrong. The pre-war study of this question was, as has already been pointed out, made inappropriate by the policy that restricted submarines to warship targets. Nevertheless no thorough theoretical or practical investigations were ever carried out.

Submarines, of course, were seldom forced into a gun action and always had the option of remaining concealed and letting the enemy go should the risk be assessed as too great. This option was taken in many cases and was justified by the vulnerability of submarines to enemy gunfire, which, with a single hit, might render the submarine unable to dive. One of our submarines, Triad, was lost during a gun action at night with the Italian U-boat Toti, when she was hit by a torpedo. Two other submarines, Shakespeare and the Greek Pipinos, were hit by return fire, their pressure hulls were holed and they were unable to dive. Both, however, managed to survive and get back to base. Other submarines that were damaged or had casualties during gun actions also survived.

BRITISH SUBMARINES AND ALLIED submarines under British operational control laid ninety fields totalling 3187 mines in all theatres during the Second World War. The great majority of these mines were of the moored contact type and only 264 were of the non-contact magnetic ground variety. The moored mines were all laid by eight submarine minelayers, which were the six British boats of the Porpoise and Narwhal classes, and by the Free French Rubis and Netherlands O1. Of these mines, fifty-two are known to have been struck by enemy vessels. The total casualties caused on all stations were a destroyer, three torpedo boats, a corvette, a small minelayer and seventeen minor war vessels (minesweepers and anti-submarine craft) which were sunk and a U-boat which was damaged. Twenty-one merchant ships totalling 42,664 tons and five fishing vessels were also sunk, and two ships of 1857 tons damaged. The ground mines were discharged from torpedo tubes and were mostly laid by T and S-class patrol submarines. Four of them were detonated by enemy ships which were merchant vessels totalling 4835 tons. This works out at 1.6% of the mines laid.

AN ANALYSIS OF THIS KIND would not be complete without some consideration of the War Patrols, missions or sorties, which were the way in which our submarines operated. We may define a patrol as a sortie for any purpose against the enemy in which the submarine operates independently, and to include independent passages through enemy waters or through waters in which the enemy may be encountered. Submarines acting as escorts to convoys, count as patrols whereas submarines attached to convoys for passage do not. Within this definition, British and Allied submarines under British operational control made a grand total of 2603 patrols during the Second World War. A total of 1064 of these were on the Home or Atlantic station, 1162 in the Mediterranean and 404 in the Far East. Of this grand total, 380 patrols were made by Allied submarines, and the rest totalling 2223 were by British boats. The Royal Netherlands Navy made the most patrols under British operational control and these amounted to 131. The French came next with 117 followed by the Poles with 49, the Greeks with 33, the Norwegians with 24, the United States with 20 and the Italians with six.

The duration of war patrols varied considerably according to the mission, the size of submarine and the distance of the patrol area from the submarine's base. The theoretical endurance of the various types of submarine proved to be fairly accurate. The longest patrol of the war by a British submarine was that made by Tantalus (Lieutenant Commander HS Mackenzie DSO DSC RN) in January and February 1945, from Fremantle in Australia, up into the South China Sea. It lasted fifty-five days and Tantalus covered 11,692 miles returning with less than 5% of fuel remaining¹¹. The longest patrol by an S-class submarine was by Sirdar (Lieutenant JA Spender RN) in November and December 1944 from Fremantle to the Java Sea, returning by Darwin. This patrol lasted 49 days and she steamed 8880 miles¹².The longest patrol for a U-class submarine was by Vivid (Lieutenant JC Varley DSC MBE RN) into the Malacca Strait from Trincomalee, lasting 22 days and steaming approximately 3300 miles. The shortest patrols made were generally those which were not planned as such and were cut short for some reason such as a defect, sickness of one of the crew, expenditure of all torpedoes or being sunk by the enemy. The shortest planned patrols by British submarines were those of the H-class from Harwich off the coast of Holland. These lasted a week or sometimes a day or two longer.

In general, patrols by our submarines were substantially less than their maximum endurance. North Sea patrols by T and S-class submarines were normally of fourteen days, sometimes extended to sixteen days or so. Home station patrols were later extended to three weeks on occasion for patrols in the Bay of Biscay and off North Norway and to five weeks for the Azores. The American submarines operating in European waters in 1943 made patrols of forty to fifty days and our own submarines, in this period, tended to be sent out for three and a half to four weeks when necessary. In the Mediterranean, patrols from Gibraltar and Alexandria were generally of three to three and a half weeks duration and were extended to four weeks in the Adriatic and northern Aegean. Patrols from Malta by the small U-class were short, often of only ten days and seldom more than a fortnight. It was mainly in the Far East that longer patrols were necessary. In the early 'phoney war' period, submarines of the O, P and R-classes were normally out for three and often for four weeks as were the 'River' class in the South Atlantic during the same period. In the Malacca Strait, operating from Ceylon in 1942-5, however, patrols were seldom more than three to four weeks and it was not until the Eighth Flotilla moved to Australia in 1944 that the S and T-class were fully extended: the T-class then did five to six weeks and the S-class four to five weeks.

The advantage of long instead of short patrols is that the proportion of time at sea spent and wasted on passage is less. This advantage was believed by the British operating authorities to be more than offset by the disadvantage of long patrols on the efficiency and morale of the crews. Whether this was true is open to discussion. American submarines made patrols of sixty days throughout the Pacific campaign without loss of efficiency or morale. Their submarines were larger and more habitable than ours, but this does not apply to the Germans, who operated medium sized U-boats across the Atlantic on the American coast and in the West Indies. U859, sunk by Trenchant off Penang, had sailed from Kiel three months before and had travelled over 15,000 miles. Rorqual did 93 days at sea out of 125 in the Mediterranean in 1940, and Trenchant 76 days out of 88 in the Far East in 1945. There was certainly no loss of morale in Rorqual or Trenchant, as both these submarines distinguished themselves in these periods. In general, it is suggested that British submarine war patrols were on the short side and they could have spent longer in their patrol areas and wasted less time on passage without loss of efficiency or morale. They need not have worried about torpedoes for out of the total of 2603 war patrols, only seven submarines returned with all torpedoes expended.

Submarine operating authorities and indeed the Commanding Officers and crews of the submarines themselves did not like being diverted to do special operations, store carrying, escorting convoys, towing X-craft or transporting chariots or anything else which took them away from offensive operations against enemy warships and U-boats and enemy sea transport. This is understandable, although on occasions, these operations contributed to the general campaign against enemy sea traffic or assisted submarines in some way. For instance, the attack on the Italian coastal railway system forced more traffic to go by sea where the submarines could attack it directly. Even store trips were of value to the submarines based in Malta, as they brought in torpedoes for them.

So it is clear that the purpose for which our submarines were designed and trained, that is for attack on warships, turned out to be a far smaller proportion of their operations than attack on merchant ships, which Great Britain had done her best to outlaw between the wars. This was mainly because the military value of the enemy's sea traffic had not been foreseen. The enemy sea traffic also allowed significant breaches to be made in our blockade, which was an essential part of our grand strategy. The enemy had, in any case, made unrestricted attacks on our commerce and there was no hope that we could encourage him to desist by not doing it ourselves. Our surface fleets were not able to prevent the enemy using the sea in his own waters mainly because of the strength of his air forces, which made it hazardous or impossible. Submarines, however, were able to contest the use of the sea in these areas and were also useful in many ways to other forces.

WE MUST NOW TURN to an analysis of the losses of our submarines during the Second World War. Of the two hundred and six submarines of the Royal Navy that were used in the Second World War, seventy-four or 36% were lost. Another seventeen submarines belonging to our Allies were also lost while operating under British control. Seven of these were from the Royal Netherlands Navy, three were French, three were Greek, two Polish, one Norwegian and one Russian¹⁵.The percentage lost of these Allied boats was much the same, actually 35%. The worst year for casualties was 1940, when a total of twenty-nine British and Allied submarines were lost off Norway and in the Mediterranean. The year 1942 came next with the loss of twenty-two boats, whereas in 1941, there were fifteen submarines sunk and in 1943 there were seventeen. In 1944-5 we only lost seven in all.

By far the greatest number of casualties were suffered in the Mediterranean, where the total lost came to forty-nine. As we and our Allies had sent 116 boats to operate in that sea, this comes to a loss rate of 42%. If we take the British total and casualties, it comes to 49% or half of the submarines employed. In Home waters and the Atlantic, thirty-four of our submarines were sunk, but ten of these had nothing to do with the enemy as will be told shortly. In the Far East, the total was eight and five of these were from the Royal Netherlands Navy. As the total number of individual submarines employed in this area was seventy, this comes to eleven per cent. If we exclude the Netherlands boats, the figure for British losses was five per cent.

We now come to an analysis of the losses by type of submarine. The highest percentage loss was of the minelayers of the Narwhal class, which with four sunk out of five, works out at 80% and only Rorqual survived the war. Next came the large elderly submarines of the O, P and R-classes with which we may group the three 'Rivers' and Porpoise, which were of similar construction with external fuel tanks. They suffered fourteen casualties out of twenty-two boats, which is 64%. The submarines designed and built in the Netherlands came next with eight lost out of seventeen or 47%. The modern British submarines of the S, T and U-classes all suffered losses of 30-32%. Fifteen out of the forty-seven T-class were sunk; eighteen out of forty-six of the S-class and twenty-one out of seventy U-class were lost. The French built boats worked out at 27% with six casualties out of twenty-two¹⁶. A miscellaneous class¹⁷ works out at 25%. The lowest casualty rate was amongst the old boats of First World War design and this category includes the submarines taken over from the USN in 1943. This worked out at four losses out of twenty-one or 19%. These submarines, however, although sent on operational patrols on occasion, were used mainly for training.

The cause of the loss of the greatest number of British and Allied submarines under British operational control was almost certainly the mine. Four submarines definitely struck mines and were lost, and this cause was confirmed by survivors. Another twenty-six boats were probably mined. All that is known of their loss is that they did not return from patrol. Post war research, which includes knowledge of the position of enemy minefields, coupled with our knowledge of the routes they took and their patrol areas show, in all these cases, that they either passed through or close to enemy minefields. There is also no evidence from enemy records of any other reason for their loss. Nevertheless, some kind of submarine accident cannot absolutely be ruled out. In one further case, the submarine definitely struck a mine but survived and was subsequently captured by air and surface forces. In another two cases, the submarine passed through an enemy minefield, but there is also another explanation for their loss, one by air attack and the other by surface attack. Lastly, one boat's loss was possibly due to a mine, but may well have been due to a submarine accident. Two other submarines definitely struck mines but survived and got home, although both were seriously damaged. Very nearly as many of our submarines were sunk by surface ships, that is, by destroyers, torpedo boats, corvettes and other anti-submarine vessels, as by mines. The total amounted to thirty boats and possibly one other, and ships had a hand in completing the destruction of yet another. The enemy anti-submarine detecting devices have been discussed in this account in a number of places. Neither the Italians nor the Japanese had apparatus for detecting submerged submarines as good as the British asdic. From 1942 onwards, however, the Italians had acquired the German echo detection set, but it was of short range and could only be used at comparatively slow speeds. They relied for initial detection on hydrophones. The silencing of machinery in British submarines from 1940 onwards was largely effective against hydrophones and in many cases of the loss of a submarine to surface ships, initial contact was obtained by some other means. Eight submarines were lost to the escorts when attacking convoys and another four are definitely known to have given away their presence by unsuccessfully attacking the anti-submarine vessel itself. In a number of the remaining cases, the hunting or patrol vessels were drawn to the area by wireless direction finding stations, or some activity in the area by the submarine. Two submarines were surprised on the surface at night, but in the rest of the sinkings by surface anti-submarine vessels the exact circumstances are not known. In most of the sinkings from 1942 onwards, however, the final destruction of the submarine was by depth charges directed by the German echo detection system. Six of our submarines were sunk by enemy U-boats, four of which were German, one Italian and one Japanese. All were torpedoed while on the surface, one during a gun duel at night. Three of those lost in 1940 in the North Sea were in their patrol areas, which, almost certainly had been revealed to the enemy by signal intelligence. Enemy aircraft only sank two and possibly three, of our submarines at sea, although they assisted surface ships to destroy three others. The Luftwaffe also sank four submarines in harbour at Malta by bombing. Finally the fate of four of our submarines is completely unknown and a search of enemy records reveals no clue at all.