Chapter 13: Cruiser-Submarine X1
1. In 1915 the Submarine Committee had though a cruiser- submarine design feasible. It was in that year the Fleet submarines of the K Class started to build. Apparently after the war the idea was taken up seriously and the 1921/22 Estimates contained a cruiser-submarine X1 which was laid down at Chatham on 2 November 1921. She was the first submarine to he designed and [aid down since the war ended in November 1918 and when completed on 23 September 1925 was the largest submarine in the world at the time. The vessel was commissioned in December 1925 and ran successful full power trials in March 1926 before acceptance in April 1926. After passage to Gibraltar and back she had main engine trouble and spent the rest of the year in Dockyard hands. After a successful full power trial in January 1927, X1 joined the Mediterranean Fleet. During a near full power trial in January 1928 further major engine troubles occurred which were repaired at Malta, but whilst on passage in April 1928 she had similar engine failures. Over this same period the auxiliary engines and HP air compressors also gave trouble. Thereafter it can be said that X1 spent most of her time in Dockyard hands.
2. There had been considerable opposition to X1 by the time she finished building. She was 'of more value to the enemy than ourselves'. As a submarine X1 was a good sea boat and handled well on the surface and submerged, but there were faults. The remarks of the Commanding Officer in December 1930 include 'internal arrangements not very satisfactory because of overcrowding with auxiliary machinery. Accommodation is cramped, ventilation poor and ship suffers from humidity, diving arrangements good, electrics satisfactory except for dampness problems. Inadequate battery ventilation, armament satisfactory, main and auxiliary propelling engines the least satisfactory feature of X1'. Whether things were in general as bad as this report suggests is open to question, but frustration with the machinery must have been most demoralising.
3. In May 1933 Their Lordships considered the question of the future of X1 and decided that in view of her age and limited operational value her retention as a potential fighting unit was no longer justified. In accordance with the London Treaty she could not be scrapped and be replaced by equivalent new construction tonnage until 1938 and it was therefore considered desirable to retain her. It was approved in December 1933 for her to be placed under Dockyard control; her main Kingstons were blanked and the vessel laid up in Fareham Creek. X1 was taken off the active list late in 1936 and scrapped in 1937 by which time the London Treaty was dead having expired on 31 December 1936.
4. It seems hardly in keeping with a period of undoubted economic restraint and with the Washington Conference in progress that a submarine of the size and complexity of X1 should have been considered. However, it was time that some new submarine designs should be undertaken.
The main objects of the design of X1 appear to have been:
- For the Admiralty to design a diesel of considerably greater power per cylinder than had been used in earlier classes,
- The practicability of installing and operating a relatively heavy gun armament capable of engaging a destroyer
- To ascertain the diving and control capabilities of a large submarine.
The main design particulars of X1 were:
|Length overall||363ft 6in.|
|Breadth extreme||29ft 10in.|
|Displacement surface||2780 tons|
|Displacement submerged||3600 tons|
|Speed surface||19.5-20 knots|
|Speed submerged||9 knots|
|Endurance surface||14 500 miles economical|
|Endurance submerged||50 miles at 4 knots|
|Torpedo tubes, bow||Six 21-inch|
|Guns||Two twin 5.2-inch mountings|
5. The form was more of a complete double-hull type than any previous British design. The external hull extended around the pressure hull to fore and aft longitudinals on top of the hull a few feet to port and starboard of the middle line. The pressure hull was completely surrounded by external tanks except at the fore end where for a few feet only the pressure hull became the outer hull. The externals were used for main ballast tanks, with oil fuel tanks on top of main tanks over the amidship portion and with four oil fuel compensating tanks amidships.
Nine WT main bulkheads each with a 2ft 9in circular door subdivided the pressure hull into compartments. Reading from forward torpedo tube compartment, torpedo stowage compartment, then three battery compartments with two officers' quarters over with a total length of about 70ft, control room, auxiliary engine room with a crew space over the forward end, main engine room, motor room with crew space over, crew space, and steering gear compartment.
Frame spacing was generally 1ft 6in except that in way of the battery tanks it varied considerably between 1ft 6in and about 2ft 0in. The pressure hull plating amidships was 1in thick.
A very large bridge was occupied mainly by gunnery control gear including an upper control room, a range finder room and a director tower. The conning tower took second place abaft these gunnery spaces. A high superstructure at bridge deck level carried one 5.2-inch twin mounting just forward of the bridge and a second mounting about 50ft aft of the bridge. The normal superstructure forward was large with three large buoyancy tanks at the forward end. Two drop keels of 10 tons each were fitted, one well forward and the other aft of amidships.
It was originally intended that X1 should be designed for a diving depth of 500 feet but this was later changed to 350 feet. The test depth was 200 feet.
6. The Loa was 363ft 6in, the Lbp 350ft 0in and the Lph about 320ft 3in. The extreme after end was a main ballast tank 26ft long.
The moulded beam and extreme beam of pressure hull amidships was 19ft 7½in and 19ft 9½in respectively with 1in plating. The maximum beam of externals amidships was 29ft 10in.
The sections amidships being circular the depth of pressure hull was as the beam. The depth moulded from the keel of the outer hull to the top of the pressure hull frame was 21ft 3¾in as designed. The overall depth would be about 21ft 5½in allowing a 30lb keel plate. The ballast keel was 15in deep so that the overall depth to underside of ballast keel (USK) was 22ft 8½in.
In the design stage the draught to the LWL from the USK was given as 15ft 9in. Later on the load draught is given as 17ft 0in. The former figure is with the normal stowage of oil fuel of 219 tons and the latter when carrying the total stowage of 452 tons of fuel.
13.4 Displacement and Stability
7. The capacity of the main ballast tanks was 841 tons and of the controlled free flooding spaces 116 tons. The normal stowage of oil fuel was 219 tons and with reserve oil fuel, 452 tons.
DNC gave the displacements as submerged 3600 tons, surface 2780 tons, Washington 2525 tons and standard 2425 tons. These figures are when carrying the normal stowage of oil fuel.
With a submerged displacement of 3600 tons and all main ballast tanks empty the surface displacement was 2759 tons and the reserve of buoyancy 34.7%. The surface displacement of 2780 tons given by DNC is with 21 tons of water remaining in the tanks and is the service displacement. The reserve of buoyancy fell to 33.7%.
When carrying reserve oil fuel the main ballast water decreased by 274 tons to 567 tons; with all main tanks empty the surface displacement was 3033 tons and the reserve of buoyancy 22.5%. The service displacement would be approx 3050 tons.
The only figures seen for stability, probably as designed, are without reserve oil fuel GM 14.3in and with reserve fuel GM 13.8in and BG 10.8in.
13.5 Speed and Endurance
8. The designed total power of the main and auxiliary engines was 8000 bhp and the corresponding surface speed 19.5 - 20 knots. Eventually the maximum power was assessed as 7000 bhp as described in Paragraph 13. On trials 7135 bhp was obtained and the trial speed is given as 19.5 knots. This would have been at the normal displacement of 2780 tons. In 1930 the speed with reasonably clean bottom was 18.6 knots when fitted with new propellers and carrying maximum fuel at a displacement of 3048 tons.
The design surface endurance was 14 500 miles at economical speed. Operational figures in 1930 were 5300 miles at 18 knots and 16 200 miles at 10 knots using 95% of the maximum stowage of 452 tons of fuel. The designed submerged speed was 9 knots at 2400 bhp. This was not achieved and 7.5 to 8 knots appears to have been the maximum.
The submerged endurance was to be 50 miles at 4 knots. In service this was disappointing and the only operational figures seen are 18 miles at 4 knots, 31 miles at 2.5 knots and 20 miles at 1.5 knots. These figures seem to be extremely pessimistic and the reason for such low figures is not apparent.
13.6.1 Main Ballast Tanks
9. There were 27 main tanks, No 1 forward of the pressures hull, No 2 in the forward end of the double hull, Nos 3-14 Port and Stbd sided in the double hull and No 15 at the extreme after end completely surrounding the pressure hull and forming part of the double hull. The total capacity of the tanks was 841 tons. No internal main ballast water was carried.
The sided tanks extended from the vertical keel to fore and aft longitudinals a few feet off the middle line in the superstructure. The upper portions of the externals in way of Nos 5-10 main tanks were built as oil fuel tanks and large trunks led from the main ballast tanks under into the superstructure, each with a 12in vent. All these tanks including the fuel tanks were tested to 15lb/in2.
Nos, 4, 5, 10 and 11 main tanks Port and Stbd were used as reserve oil fuel tanks and when so used the main ballast water available decreased to 567 tons.
There were three buoyancy tanks forward in the superstructure with a total capacity of 116.5 tons. They were tested to 10lb/in2 only and were controlled free flooding spaces as designed. Their capacity was not included in the total of main ballast water used. It is probable that in due course HP blows were fitted to these tanks in which case they would become main tanks. The only difference to the figures given in Paragraph 7 would be an increase in submerged displacement to 3716 tons.
13.6.2 Oil Fuel Tanks
10. A total of 219 tons of oil fuel was carried in three internal tanks (40.5 tons) in the auxiliary engine room and eight external tanks (178.5 tons), four each Port and Stbd in the double hull above main ballast tanks Nos 5-10. This was originally the normal stowage.
In addition main ballast tanks Nos 4, 5, 10 and 11 Port and Stbd were fitted to carry reserve oil fuel. These tanks held 233 tons of oil fuel of sg 0.88 making a total of 452 tons.
13.6.3 Other Tanks
11. Other named tanks were fitted generally as in previous classes except as follows:
- Four compensating tanks amidships in the externals (68 tons) for compensating oil fuel. Although tested to 50lb/in2 it was probably necessary to back up these tanks with HP air when diving deep.
- A buoyancy tank amidships (10.5 tons) tested to 100lb/in2; this would have been used as a statical diving tank.
- Nearly 50 tons capacity in ten tanks, four for lubricating oil, two for piston oil and four as bearing oil drains.
- Shell compensating tanks (approx 4.5 tons each) Port and Stbd sides of each 5.2-inch magazine.
- The cable lockers were in the externals.
There was over 100 tons of tank space for auxiliary ballast, trimming and adjusting water which was ample to allow for any possible changes in sea water density likely to be encountered.
13.7 Main Machinery
12. X1 had twin shafts and the machinery consisted of:
- (a) Two eight cylinder diesels, each developing 3000 bhp at 390 rev/min.
- (b) Two auxiliary engines (ex German U126), developing 1200 bhp each. These auxiliary engines (charging engines) drove (c).
- (c) Two generators which could charge the battery and also drive the main motors direct.
- (d) Two main motors which could develop 1000 bhp each when driven by the generators when the latter were driven by the auxiliary engines working at full power.
13. Each shaft carried a main engine and a twin armature main motor and working together the design surface power was 8000 bhp. However the auxiliary engines did not develop 1200 bhp each side and in consequence the shaft revolutions were reduced and the main engines could not develop full power. The total bhp was therefore taken as 7000 and the corresponding full surface speed as 19.5 knots. Later on figures of 6000 bhp and 19 knots speed have been seen, but this was undoubtedly using the main diesel engines only. For further details see Chapter 25 Paragraphs 29-30
14. As explained in Paragraph 12, each twin armature main motor could be driven by its generator for surface running or from the battery. When being driven by the generators the maximum bhp could not exceed 2000; when running from the batteries 2400 bhp could be obtained.
The main battery of 330 cells was split into three sections of 110 cells each in a separate battery tank. They were large cells each weighing 1475lb, as against the normal size of about 950lb, giving a total weight of battery of 221 tons.
15. The torpedo armament was six 21-inch bow tubes and a total of twelve Mark IV SX torpedoes.
16. Four in number 5.2-inch guns in twin mountings were sited one mounting forward of the bridge and the other about 50ft aft of the bridge. A circular gun trunk of about 4½ft diameter ran from the mounting to the magazine directly below in the lower half of the pressure-hull. A 10ft diameter-working chamber surrounded the gun trunk between the gun deck and the top of the pressure hull. Each magazine carried 100 rounds of ammunition per gun and shell compensating tanks were fitted each side abreast each magazine.
17. The gunnery control arrangements occupied most of the bridge space. From the pressure hull a hatch led into an upper control room on the top of which was the director tower extending to about bridge canopy height. The cover of the director tower could be raised vertically two feet and when closed was obviously watertight to full diving depth. A second hatch from inside the pressure hull led to a range finder room alongside the upper control room and a 9ft range finder was fitted on the bridge aft of the director tower. The conning tower was abaft these gunnery spaces and access was provided from the conning tower to the gunnery rooms.