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The A Class Submarine

In a personal minute to the Board of Admiralty dated 14th June 1941 the Prime Minister (Mr Winston Churchill) called for a new submarine programme to meet the turn of events which the war had taken. Numbers and speed of construction were to be primary factors as the vessels would be required principally for short-range work to resist invasion and impose blockade. However, this first call for a war design submarine led eventually to the A class, a general purpose submarine capable of high surface speed and long endurance suitable for operations at home or abroad.

In late June 1941, Admiral (Submarines) requested DNC to give consideration to proceeding with a new design of a small submarine for attack on merchant ships, the intention being that the construction should not interrupt the existing submarine programme. The main requirements of the design were a maximum surface speed of 17kts with a cruising speed of 15kts under patrol conditions in order to overtake merchant ships. This was to be achieved with an existing and tried type of engine. Four bow internal torpedo tubes and a stem tube, internal or external, a 3in gun, diving depth 300ft and an endurance of 6000 miles at 10 kts on the surface in ideal conditions were also to be provided. Three sketch designs were prepared closely resembling the 1940 S class but with a smaller torpedo armament.

The Controller also, about the same time, called for a new design intended for coastal defence or anti-invasion purposes and three other designs were prepared. These were all about the same,

• Length 160ft 0in
• Displacement 430 - 490tons
• Shp 1000
• Surface speed 13 1/2 kts
• Submerged speed 7 1/2 kts
• Endurance 3000 - 3500 miles at 9 kts

All six sketch designs were considered by the Controller and Admiral (Submarines) at a discussion in July 1941 and it was agreed that the latter three designs would be of little use as anti-invasion submarines owing to their limited operational scope and the former three designs offered little advantage over the 1940 S class and they were not progressed further.

At this meeting it was suggested that a new type (ML) diesel engine capable of 3300hp should be designed with the object of incorporating it, should the circumstances demand, in a new design of submarine capable of 18kts surface speed and superseding the S and T class.

The staff requirements for such a design were drawn up and approved in October 1942, the new class being designated A class. These requirements embodied improvements rendered necessary by war experience, e.g. higher surface speed, up-to-date radar, improved habitability for operations in the Far East, including air conditioning and increased fresh water capacity, and much longer surface endurance to cover the distances from base to patrol areas at high speed. To achieve the increased diving depth of 500ft which was required, circularity of the hull was essential, and consequently only four bow internal tubes could be fitted, with two external tubes fitted to make up the salvo of six that was also required. On the other hand, whereas the staff requirement for stern torpedo fire was laid down as two internal and one external tube, the final arrangement included two external tubes aft in addition to the two internal ones.

The ability to charge batteries whilst submerged was included in the requirements to counter the rapid improvement in radar taking place at that time, and consideration of the introduction of auxiliary diesel generators to achieve this was suggested. It was later decided that 'submerged dieseling' need not be arranged as it was considered to be of no operational value to British submarines at that time. A requirement for such equipment under the name of 'Snort' arose later in the war when the earlier ships of the class were in production, the intention then being for it to be fitted by Depot ships in the Far East, should the circumstances demand it.

The design proceeded with the utmost speed and was approved in February 1943.

Increased endurance was obtained by carrying oil fuel in tanks under the forward battery compartment and arranging for a pair of main ballast tanks to be capable of carrying oil fuel as an emergency measure. Legend particulars were as follows:

• Length overall 277ft 9in
• Breadth extreme 22ft 3in
• Surface displacement 1360 tons
• Submerged displacement 1590 tons.
• Shp main engines 4300
• Max surface speed 19kts
• Oil fuel Internal 61 tons
  External 105tons
• Surface endurance 12200 miles at 10kts, or 15200 miles at 10kts with 48 tons fuel in No 4 main ballast tank
• Shp main motors 1250 Max
• Submerged speed 8 kts for 1 hr
  Submerged endurance at 4kts - 20hrs
• Guns 1 - 4in + 1 Oerlikon
• Diving depth 500ft
• Complement 60
• Torpedoes Forward 4 internal + 2 external tubes - 6 re-loads
• Torpedoes Aft 2 internal + 2 external tubes - 4 re-loads

Arrangements were made for four of the class to be fitted with Admiralty 6 cylinder engines instead of 8 cylinder engines as for the rest of the class due to difficulties of supply. This reduced the Shp to 3400 and the maximum surface speed to 18kts.

Bow shutters were fitted to the underwater torpedo apertures forward to enable the speed of 18 1/2kts to be attained. They had to be sufficiently robust to with stand heavy weather.

Full attention was paid to the reduction of waterborne noise from the propellers and from auxiliary machinery, having regard to the great advances made in this field of detection.

As the design proceeded the after end was made slightly larger and the overall length increased to 279ft 3in. The submerged displacement increased during building to 1620 tons.

To ensure rapid production most of the submarine was mocked up, this mock up being built at Messrs Vickers Armstrong, Barrow. The engine room for the Vickers 8 cylinder engined vessel was not mocked up and the mock up of the engine room for the Admiralty 8 cylinder engined vessel was built at Messrs Cammell Laird.

Arrangements were made for all shipbuilders to view these mock-ups and to work to the same drawings. Arrangements were also made to facilitate the supply of large hull items, usually sub-contracted out, to the best advantage of all builders. This rested in a choice of sub-contractors suitable to all shipbuilders, having regard to capacity, transport, etc. The extent to which ship's fittings and pipe work could be sub-contracted out to the same firms by all shipbuilders was investigated. Arrangements were made by all the main shipbuilders to introduce a degree of prefabrication into the construction of these vessels.

Forty six vessels were at first ordered, viz. 21 from Messrs Vickers Armstrong, Barrow-in-Furness, 6 from Messrs Cammell Laird, 5 from Messrs Scotts S&E Co, 6 from Messrs Vickers Armstrong Ltd, High Walker and 2 each from Portsmouth, Devonport and Chatham Dockyards. The Vickers vessels were to have the Vickers type 8 cylinder supercharged engines and the remainder the Admiralty type 8 cylinder supercharged engines, except for the vessels at Portsmouth and Devonport which were to have Admiralty 6 cylinder super charged engines. The building cost of a typical submarine was £450,000.

The changes in the war programme at the end of 1944 led first to a proposal for an additional twenty vessels but orders were never placed. Later, as the war progressed, the need for submarines was not so great and thirty of the forty six vessels ordered were cancelled. Building details of the remaining sixteen are given in the table at the end of this chapter. Of the cancelled vessels only two, Ace and Achates at Devonport were well advanced and the hulls of these were used in ship target trials after the war.

The first vessel completed, Amphion, was delivered from Messrs Vickers Armstrong, Barrow, on 27th March 1945. On first of class trials this vessel achieved nearly 18 1/2kts on the surface and almost 8kts submerged, a much quicker diving time than previous classes, and satisfactory performances as regards change of depth, turning and endurance. A deep dive to 600ft, 100ft beyond the designed operational depth, proved entirely satisfactory and except for certain modifications to the periscope supports to prevent vibration, the class appeared to be acceptable for operational duty.

Later experiences in Amphion and Affray indicated the necessity to dispose of some of the external oil fuel tanks and fit a bow buoyancy tank to improve seaworthiness.

Prefabrication of the pressure hull of all vessels was carried out to a high degree, electric welding being employed, to the complete omission of riveting, throughout the hull, external tanks and casings. The pressure hull was built of S quality plating and was of circular section throughout, fabricated in cylindrical lengths amidships and conical lengths at the ends. The bulkheads at the ends of the pressure hull were specially constructed of dome shape.

As the design progressed and during building of the earlier ships of the class continual revision of the radar requirements was necessary to keep in step with developments in radar. The design originally envisaged a single rotating mast carrying a type 29 1 W array for aircraft warning only. Finally two masts were provided, both rotating, one for aircraft warning and the other for surface warning, the combined equipment being designated type 267MW.

The up-to-date version of this equipment, fitted as an A&A in all ships of the class, was known as type 267PW which still entailed two masts but possessed much improved performance and enabled the habitability of the radar office to be improved. The installation of these two masts and their associated equipment together with improved plotting and fire control arrangements necessitated a rearrangement of the entire control room, the details of which were settled by means of a mock up. A similar arrangement of control room was followed in T class vessels fitted with this up-to-date equipment.

In the design of the ventilation system a radical departure from previous practice was made by the omission of a separate exhaust system. Except for the radar office and galley, all compartments were ventilated by forced supply and natural exhaust, the supply fans being sited with coolers, compressors and condensers in a special air conditioning compartment directly below the control room. These fans were supplied with air through the hatch to this compartment and delivered it, dried and cooled by the Freon system if necessary, through punkah louver's, via two main supply bunks, one running forward and the other aft. Two Freon units, each of 55,000btu/hr capacity, were fitted for air conditioning and this proved, by sea experience, to be adequate to maintain equable air conditions in vessels of the size of T or A class.

In the later stages of building of the earlier vessels of A class, and S and T class, provision was made for fitting the newly developed air purification plant consisting of special 'silent running' carbon dioxide absorption units and of generators for burning oxygen candles to maintain an acceptable concentration of oxygen in the air while submerged.

In accommodation arrangements, also, A class departed from practice in previous vessels. The commanding officer had a cabin, which was built, as a separate pressure tight chamber in the bridge structure and reached via the conning tower. All the messing and sleeping quarters for the crew was grouped forward between the control room and torpedo stowage compartment and the galley and WCs were placed abaft the control room near to the engine room. The 12* Achates was lowered to collapse depth after the war. She failed at 977ft compared with a calculated figure of 960ft.

WCs were gravity drained to a special drain tank, which could be blown when a suitable occasion arose without tear of disclosing the position of the submarine to the enemy.

Two major modifications were found to be necessary after trials. The first of these was due to an unacceptable vibration of the periscopes at speeds above 2 1/2kts. The method of support had been changed due to the introduction of the CO's cabin and a longer periscope overhang than was usual had been allowed. The vibration was traced to the alternating eddy forces on the periscope tubes and standards and this was aggravated by insufficient rigidity in the support itself and in the connections.

The trouble was overcome by increasing the height of the standards to decrease the overhang and by stiffening up the supports. Similar modifications were made to the periscope and radar mast.

The second was made necessary because the rolling motion in certain conditions of swell and sea was found to be very unpleasant. The fundamental causes of this were proved, after lengthy investigations, to be due to a combination of effects arising from the fulfilment of the staff requirements. The requirements for high speed low silhouette and quick diving acted adversely on seaworthiness, more so than had been appreciated in design. The motion was considerably improved by redisposing some of the external oil fuel tanks in relation to the main tanks to lower the position of the centre of gravity, by fitting a bow buoyancy tank and subdividing the main tanks into port and starboard tanks by fitting a bulkhead in the ballast keel (formerly the main tanks were continuous from one side to the other and this allowed water to move freely from side to side in a seaway).

Another modification found necessary was the provision of more store space. This was obtained by using one of the forward fresh water tanks as a store. The fresh water capacity was thereby reduced to 63.5 gallons per man and this was accepted in view of the fact that distillers were fitted.

The question of running the diesel engines when submerged was reopened late in 1944, in view of the progress made by the Germans with the 'Schnorkel' apparatus and bearing in mind possible requirements in the Far Eastern theatre. A set of 'Snort' gear based on German design was tried in Truant in 1945 with success and arrangements were made to fit all of the A class and most of the other submarines with this gear. This programme was slowed down very considerably with the cessation of hostilities.

High Speed Target Submarines

Early in 1944 reports were being received of a new type of German submarine with a 'streamlined' hull form and reported to be capable of 20kts on the surface and 16kts submerged. This high submerged speed was a very considerable increase over the normal. 8/9kts of the conventional type and constituted a considerable menace. In order to develop counter measures to such a high speed craft, it was considered essential to carry out exercises with a submarine of comparable speed. (The efficiency of the Asdic equipment against high speed submarines needed to be checked and new attack tactics developed).

Accordingly DNC looked into the question of converting a British submarine to high speed by' cleaning up' the hull and casing, blanking torpedo tube apertures, removing the guns etc, fitting a smaller streamlined bridge, removing a periscope and the radar masts, rating up the motors and fitting higher capacity batteries. This was investigated for both U and S class. In view of the urgency it was decided to convert the S class submarine Seraph. Minor modifications to the hydroplane gear were required and T class propellers (which had a bigger pitch) were fitted. The conversion was completed at Devonport within two months, the target date being end August 1944.

The converted Seraph carried out First of Class Trials in September 1944. These trials were entirely satisfactory and she achieved a speed at periscope depth of 12.52kts at 411 rpm and 1647bhp as compared with 8.82kts at 406rpm and 1460bhp obtained by an unconverted sister submarine Sahib, on First of Class Trials. On the surface Seraph achieved 16.75kts at 460rpm and 92 galls/fuel/hour as compared with 14.56kts at 464rpm and 86 galls/fuel/hour before conversion. Seraphcompared very favourably with the rest of the S class as regards underwater control but, as was expected, the diving time was considerably increased due to the deliberate reduction in free flood holes.

The resistance of the converted Seraph was estimated to be 55% of that for the unconverted vessel.

Later Sceptre, Satyr, Statesman, Selene, Solentand Sleuth were also converted to similar high speed targets.

Improved A Class Submarines

In the latter part of 1944, Admiral (Submarines) and the Technical Departments held discussions on the possible trend of future submarine design, particularly as regards submerged speed, diving depth, duration of submergence and lessons learnt as a result of the war. Admiral (Submarines) then put forward a proposal for three submarines to be built on the lines of the A class incorporating the most up to date equipment and improvements arising from war experience. The modifications which were envisaged, such as improved 'Snort' arrangements, increased space in the control room and at the ends of the vessel around the torpedo tubes, and improved surface performance, could only be effected by a redesign.

Whilst this was progressing, information was continually forthcoming regarding German designs for high submerged speeds, and especially information on the hydrogen peroxide turbine (Walther turbine). In July 1945, Admiral (Submarines) expressed the opinion that the three operational submarines, which had been included in the 1944 programme, should represent a radical change from the A class and should be designed around the Snort at the sacrifice of surface qualities, amounting indeed to surrender of gun power and the acceptance of comparatively moderate surface speed. He also considered that the design should be such as to incorporate, at some future date, a new type of propulsion unit capable of developing the high power necessary to achieve submerged speeds much in excess of that possible by either 'Snort' or batteries. In the light of these views, DNC embarked upon a new sketch design, incorporating novel Snort arrangements and with high battery capacity, in order to obtain a maximum submerged speed well in excess of that of orthodox types of submarine or that possible by 'Snort', though not comparable with that possible with the hydrogen peroxide turbine.

The design had not been developed very far when views changed once more. The statement of broad staff requirements for these submarines prepared by Admiral (Submarines) called for the definite incorporation of a high power propulsion drive in addition to normal propulsion methods. The design of the high battery power submarine was therefore terminated, as few details of the peroxide turbine were known. Soon after this the three operational submarines were cancelled and replaced, in the 1945 (revised) programme, by an experimental type of submarine using the hydrogen peroxide turbine, with the object of obtaining experience with the turbine and in the control and other problems of high speed submarines.

Moving on 55 years the new Class of 'A' boat is a far cry from those boats designed during and just after the 2nd World War. Particularly as regards submerged speed, diving depth, duration of submergence and a new type of propulsion unit capable of developing the high power necessary to achieve submerged speeds much in excess of that possible by either 'Snort' or batteries of the WWII boats. The advent of the Nuclear Submarine has changed the whole concept of Submarine warfare, for many people, not always for the better.

Previously the heads had to be flushed each time they were used and the compressed air needed would make a visible bubble. It could also backfire? known as, getting, your own back'.

This requirement led, eventually to HMS/M Explorer & HMS/M Excalibur known as for good reason as Exploder & Exciter.

The new Nuclear class Submarine displaces 5900 tons and with a submerged speed in excess of 30kts