Chapter 28: Gun Armament
1. D4 was the first British submarine to be fitted with a gun and it is claimed that she was probably the first submarine to carry a gun. In the sense that it was a tried and effective weapon this claim may be correct. But the idea was not new.
The first USN submarine, a Holland type purchased in 1900, was designed to carry an armament of three tubes-two in the bow and one at the stern. Fyfe states that 'two were made to throw aerial torpedoes and shells, whilst the third was to discharge Whitehead torpedoes. The submarine gun aft, which was worked by pneumatic power and was capable of throwing 80 Ib of dynamite a distance of about half a mile, was however abandoned. The aerial gun at the bows is 11. 25ft long and 8in in diameter and each of the projectiles weighs 222 Ib and carries 100 Ib of gun-cotton. The gun can shoot these projectiles a distance of one mile'. Whether this gun was ever fitted and used is not known, but for a boat of 75 tons displacement and 53ft l0in. long (i. e. smaller than the RN Holland ) already carrying one torpedo tube it is extremely doubtful whether it was really practicable. Fyfe made his statement in 1902 when information about submarines was kept very secret so it is possible that this gun was a design idea only.
2. However D4 was fitted with a serviceable 12-Poimder gun when completed in November 1911 at Vickers. Since this was obviously an experiment no magazine was fitted.
The mounting could be housed in the superstructure in a non-watertight, casing. It was operated by compressed air, the mounting being placed on a pneumatic ram for lowering and raising the gun and cradle. Watts states that 'doubt was ex-pressed whether the delicate mechanism of the mounting would survive but experience appears to have shown that effective measures can be taken to prevent undue corrosion'. This was after original troubles had been remedied. At first it was found that the mounting was unsatisfactory 'due to erosion' and it was therefore approved that a gun should not be fitted in the remaining D Class or in the E Class vessels then ordered.
3. At a conference held in October 1912 Commodore (S) expressed the opinion that the 12-Pounder gun of D4 should be developed with a view to adoption in the overseas type submarines which had been recommended by the Submarine Committee earlier that year. He also expressed the view that a l¼-Pounder pom-pom would suffice for the D and E Class, of the kind developed by Vickers for use in aeroplanes and airships. His intention was that the gun should be kept inside the boat and hoisted up the conning tower when required.
4. There is no doubt that at this time it was intended to fit a gun of some sort as soon as a suitable weapon could be developed. Magazines were allocated during building in E1 onwards but it is difficult to determine when guns were actually fitted and the type. From Vickers records it would appear that only the last six boats completed at the yard i. e. E19-24 between July 1915 and January 1916 were fitted with a gun before leaving Barrow. E19 had one 2-Pounder, E20 a 6-inch Howitzer and E21-24 one 12-Pounder and a 2-Pounder. There would have been a shortage of mountings and they would not necessarily have been given to new construction.
5. At the beginning of the war the 12-Pounder was the specified submarine gun, but the ensuing war years brought experiment and change. Very soon in the design stage an alternative gun armament was given of a 12-Pounder or a 3-inch HA gun. The G Class had the latter on completion in late 1915. E11 carried a 6-Pounder and by 1918 E12 had a 4-inch gun. There was no set pattern in any class and it would be expected that the type of gun fitted was changed in some individual vessels.
6. Going back to 1914 the 12-Pounder in D4 was undoubtedly developed to overcome its initial teething troubles. It was usually sited on the casing top forward of the bridge and was of fixed type (not housing as in D4 originally) with 100 rounds of ammunition in a magazine forward.
The 2-Pounder was probably a development of the 1¼-Pounder mentioned in Para. 3. In time most submarines carried one of these weapons in addition to any other gun. It was portable.
7. Of the other classes laid down before 1914 the S Class, V Class, W Class and F Class were not designed to carry a gun and did not have one as built. It is stated that the V Class had a 12-Pounder fitted after completion and this may have applied to the other classes. They did carry a portable 2-Pounder.
Nautilus was to have a 12-Pounder gun but before completion this was changed to a 3-inch HA. It was fitted just forward of the bridge and could be raised and lowered on a vertical ram to stow within the superstructure.
8. Swordfish was laid down in February 1914 and two 3-inch guns were in the design. One was fitted on the casing well forward over the forward torpedo room and the other well aft abaft the engine room. The novel feature was that they were of the disappearing type and the gun houses were watertight with the guns housed. A sketch of the arrangement is shown in Fig 28. 1. The gun was raised by the action of a hydro-pneumatic cylinder and lowered by releasing the air-pressure. A hatch at superstructure top level just abaft each gun allowed for passing ammunition close to the gun from inboard. See Fig 27. 4. The total ammunition carried was 150 rounds.
9. In the design stage of the G Class a 12-Pounder gun was specified. About 1915 this gun appears to have been superseded by the 3-inch HA gun. In the G Class the 3-inch QF HA gun was on the superstructure forward of the bridge of the same disappearing type being fitted in the Swordfish although without the watertight hood. A 2-Pounder was also carried but this is the only class for which drawings have been seen which show a fixed pedestal built on a superstructure aft of the bridge for this gun. The gun itself was portable for stowing inboard.
10. As originally designed the J Class had one 3-inch HA gun and one 2-Pounder. As built some had the 3-inch gun and others a 4-inch gun. By the end of 1918 all vessels of the class had a 4-inch except J3. Carrying a 4-inch gun increased the complement by three.
11. The first boats of the K Class had two 4-inch mountings on the main deck one well forward of the bridge and the other aft of the funnel superstructure and one 3-inch mounting at bridge deck height between the bridge and the forward funnel. The freeboard to the main deck at full surface buoyancy was only just over 5ft and the 4-inch guns especially the forward one must have been very wet with the vessel underway. A major modification was made after sea experience. The two 4-inch guns on the main deck were removed and one only replaced on the top of the funnel superstructure between the funnels. In some vessels this 4-inch mounting appears to have been fitted on a raised superstructure built just forward of the bridge.
One magazine was right forward and a second right aft. The ammunition routes were long. The magazines stowed 175 rounds of 4-inch and 100 rounds of 3-inch ammunition.
It was intended originally to fit two 5. 5-inch guns on the main deck, one forward and one aft, in this class. An official DNC drawing has been seen with this arrangement modified in red to two 4-inch guns and one 3-inch gun for K1-14. However K15 and K16 were still to have 5. 5-inch guns. This may have been the intention at the time but it is doubtful whether it was carried out since 5. 5-inch guns were certainly not in K15 and K16 in 1919.
12. It was intended that L1-8 should have two 3-inch guns but this was dropped and one 3-inch HA disappearing mounting fitted in lieu. It was sited on the casing top some way forward of the bridge and housed into the superstructure. LI, 2 and 7 the first three boats and only ones completed in 1917 were so fitted. A change then took place. Experience in the K Class with mountings on the superstructure may have been one of the reasons. In addition some experience with this type of mounting in the G Class would by now have been obtained. It was undoubtedly a complicated mounting and maintenance may have been considerable. But the main reason for the change was one of policy to enable the submarine to attack as quickly as possible an enemy submarine out of torpedo range but within gun range with the boat floating at low buoyancy. A gun access trunk was not fitted in the L1 design and passing ammunition to the gun platform via the conning tower hatch was a time consuming process.
For L9 the revised design included a gun deck at the fore side of the bridge at bridge deck level with a 4-inch gun on a revolving platform. A gun access trunk was fitted. Efforts must have been made to include these new arrangements in the earlier boats not too far advanced. There was undoubtedly a shortage of mountings. Vickers, on completion of their boats, give L3 and L12 a 4-inch Mark PXIII, L14 and L17 a 4-inch Mark IX, L18-23 a 4-inch (Mark not given) and L11, 24-25 none. However all boats eventually got a 4-inch gun of some sort which brought an increase in complement of three men as against the complement as designed with a 3-inch gun.
However, the high position of the gun did increase silhouette. Invisibility was of particular importance in the minelayers which might be forced to lay their mines in surface trim and in which the necessity for secrecy rendered the use of a gun improbable. For these reasons it was decided to remove the gun from the minelayers where fitted as being unnecessary and increasing their visibility and underwater resistance. The guns and gun trunks already fitted in L14 and L17 were removed. L24-27 were not fitted.
Another reason given for not having guns in the minelayers was 'to find space for fitting battery cooling plant'. The magazine was probably used for this purpose. It is unlikely however that the fitting of this plant was restricted to the minelayers. It is probable that a compromise was reached in other boats by using a part of the magazine for the cooling plant. It has been noticed that the number of rounds of 4-inch fixed ammunition carried decreased from 56 in the early boats as built to 36 in the later vessels of the class.
In addition one 3-inch HA gun which could be stowed in the superstructure was fitted aft with a separate magazine to stow 72 rounds of ammunition.
14. No gun was carried in the H Class, but it was originally intended to fit a 4-inch gun on a superstructure forward of the bridge in the R Class. The gun deck and structure was built in some boats but it is doubtful whether the gun was carried during the very little war service the early boats had. The gun would have had an adverse effect on submerged speed which was the main characteristic of the design. It was removed where fitted.
15. Based on experience in the K Class, K26 had three 4-inch guns (20 elevation 9000 yards range) at bridge deck level, one just forward of the bridge, one just aft of the bridge and the other aft of the after funnel. The forward and the aftermost mountings were on revolving gun platforms. A gun access trunk was fitted for each gun.
16. The L50 design was a development of the L Class with improved torpedo and gun armament. Two 4-inch guns were fitted one forward of the bridge as in the L Class and the second at bridge deck level aft of the bridge.
18. The design of the overseas patrol submarine Oberon, laid down in March 1924, included one 4-inch gun on a gun deck forward of the bridge at bridge deck level as in the L Class. Later that year the Naval Staff considered the types of submarines and their requirements to be built in future programmes. The question of guns was discussed and of course opinions varied. Details of these discussions are given in Chapter 12 Paragraph 16 to 19 . The outcome for overseas patrol submarines was a gun armament of one 4-inch or 4. 7-inch gun, the latter being considered the most suitable; AA arrangements other than Lewis guns were not necessary.
In fitting a gun some points had to be considered which may now seem obvious. If a gun was fitted at all it was primarily a weapon for surprise attack. From this point of view alone the gun and gun access hatch should be fitted as high as possible to bring the gun into action in the quickest time. Consideration of silhouette and stability limited the height at which it could be placed and, at that time, minimum silhouette was considered by many to be a priority requirement.
The gun tower hatch being for manning and evacuating the gun and for the passage of ammunition must be at a reasonable height above the waterline when in the lowest buoyancy condition in which the gun can be fought. The gun tower must also be tall enough for the ammunition number to stand in between the upper and lower hatches otherwise the passage of ammunition is slowed up and the quick closing of the hatches prevented.
19. The Odin Class had a 4-inch Mark IV gun (maximum elevation 20 range 9600 yards) as in Oberon. It was intended that in time the 4-inch guns in Oberon Class and the Odin Class would be replaced by 4. 7-inch guns. A 4. 7-inch gun was fitted for the first time in Perseus -the first of the Parthian Class, although most boats of that class appear to have been built with a 4-inch. The Rainbow Class had 4. 7-inch guns, but the bridge in that class had been lowered by 1ft 6in and the gun platform by 3ft 2in from the two previous classes. This made the bridge much wetter and flared plating was fitted round the gun platform to decrease spray on both the bridge and gun platform.
Soon after completion of the first boats of the Rainbow Class there were complaints about stability in the low buoyancy condition. As a result of trials a minimum metacentric height in the low buoyancy condition was laid down in consequence of which the 4-inch gun was adopted for all three classes and the 4. 7-inch removed where fitted. In fact the 4-inch gun became the standard weapon for all large submarines. Where fitted in the Thames Class and Porpoise Class the 4. 7-inch gun was removed and replaced by a 4-inch QF gun with 120 rounds of ammunition.
20. The Staff Requirements for the Swordfish Class included one 3-inch HA disappearing gun and in the design it was sited on the superstructure casing just forward of the bridge. It was made disappearing to cut down the resistance submerged. The gun platform was then raised 2ft 9in. at the request of RA(S). The first two vessels were so built.
On trials it was found that the resistance of the gun was less than originally thought. The gun was heavy and complicated and after a short time in service it was found that the mounting was unsatisfactory. Furthermore in the first boats so built the stability was less than as designed and listing occurred when surfacing. The answer to these points was that the 3-inch disappearing mounting was removed and a 3-inch fixed mounting fitted on the casing as in the original design, although there were many submarine officers who considered a gun in this class to be unnecessary. This change saved about 6 tons in top-weight and gave improved surfacing and reduced maintenance with little effect on submerged speed.
21. A number of experiments have been carried out over the years to find the effect of shell fire against submarines and it is perhaps appropriate to end this chapter with a brief statement on the beginning of these investigations in 1911.
Holland No 3 (or No 2 ) was sunk by shell fire during experiments inside the Skerries on 25 April 1911. Details are not known but they were undoubtedly the first experiments of this nature carried out on a British submarine. Whichever of No 3 or No 2 it was, the boat was raised. Both these vessels were sold in 1913.
On 17 October l9l2, 6-inch Lyddite shells were fired at Holland No 4 with the boat 15ft below the surface. The vessel was sunk by water flooding through a fractured glass light in the conning tower caused by the second shell bursting directly over the submarine. The vessel sank within half an hour. The conclusion, rather optimistic it is felt, was that 'if the hull is 12-14ft below the surface a 6-inch Lyddite shell cannot do any damage beyond causing the conning tower lights to leak'.