The quarterdeck of Indomitable c. 1911, shortly after a coaling session and a welcome rest for the stokers no doubt.
Indomitable at sea 15 July 1908, bound for Quebec, taking HRH the Prince of Wales to Canada for tercentenary celebrations. The Royal Standard flies from the topgallant mast.
Turrets were given 2½in–3in on the roofs and sides, faces and backs were 7in. The main deck was ¾in from the stem to the forward belt bulkhead after which it increased to 1in. Lower deck thickness ranged from 1½in to 2½in, the crown being at waterline level and the lower edge being at the lower edge of the armoured belt, 3ft 10in below water. The 2½in ran on the slopes with 1½in on the flat between the belt bulkheads. Outside these bulkheads it was 1½in forward and 2½in aft.
The forward conning tower had a 10in face and a 7in rear which was located below the bridge level. The spotting and signal tower at the rear of the conning tower was 3in on the sides with a 2in roof and floor. The communications tube had 4in plates. The torpedo conning tower on the after superstructure was 6in on the sides with a 2in roof and floor; the tube was 3in. There was a lower conning tower aft, below the main deck, which was given 2in protection. The magazine screens for limited torpedo protection were 2½in thick, and were fitted longitudinally port and starboard abreast the forward, amidships and after magazines.
Machinery
The early designs all provided reciprocating machinery, although some Members of the Board were optimistic about the fitting of turbine machinery in the cruiser type. Fisher had stressed that the importance of maintaining superiority over enemy cruisers in speed as well as armament was paramount, and as it was anticipated that new foreign cruisers might be designed with speeds of up to 24 knots, it was considered necessary to exceed this figure. The completed vessels were all fitted with Parsons direct drive turbines and four screws. The high pressure turbines were fitted on the wing shafts and the low pressure on the inner shafts. There was one HP ahead and astern turbine on each shaft, also, one LP ahead and astern turbine fitted to each inner shaft. The cruising turbines were also fitted to the inner shafts. On completion these ships had the most powerful turbine installation of any warship afloat, and were easily the fastest heavy cruisers in the world.
INVINCIBLE CLASS: PARTICULARS, AS COMPLETED
Construction
Displacement (tons), 1909 figures
Inflexible: 17,290 (load), 19,975 (full load)
Indomitable: 17,410 (load), 20,125 (full load)
Invincible: 17,420 (load), 20,135 (full load).
Dimensions
Length: 530ft pp, 560ft wI, 567ft oa
Beam: 78ft 8½in
Draught: 25ft 1in (load), 26ft 8in (full load)
Freeboard: 30ft forward, 21ft amidships, 17ft aft.
Armament
Eight 12in 45cal Mk X; Mk VIII mounting (Indomitable and Inflexible only, see Gunnery Notes)
Sixteen 4in 45cal Mk lll (one 3in AA added in Invincible 1914)
Seven MG
Five 18in torpedo tubes (four beam, one stern); twenty-three torpedoes plus six 14in for the boats.
Director control
None fitted as completed.
Armour
Main belt: 6in amidships; extending 7ft 5in above water-line, 3ft 10in below (at normal condition)
Bulkheads: 7in forward, 6in aft
Forward belt: 4in
Turrets: 7in face and sides, 3in roof
Barbettes: 7in through to armoured deck where they reduced to 2in
Decks: main 1in–¾in, lower 2½in–2in–1½in
Conning tower: 10in face, 7in rear, 2in roof and floor
Communications tube: 4in
Spotting and signal tower: 3in sides, 2in roof and floor
Torpedo conning tower: 6in sides, 2in roof and floor
Communications tube: 3in
Magazine screens: 2½in.
Machinery
Four sets Parsons direct-drive turbines, four propellers
Thirty-one Yarrow large-tube boilers, 250psi (normal), each fitted with five (Indomitable four, Inflexible three) single-orifice oil sprayers (180psi per hour per burner, Invincible; 300psi per hour per burner, Inflexible)
Total heating surface: 103,880sq ft
Grate area: 1,750sq ft
Length of boiler rooms: (1) 51ft 11in, (2) 34ft 1in, (3) 33ft 11¾in, (4) 33ft 10¾in
Length of engine rooms: 76ft
Fuel: 1,000 tons coal min., 3,084 tons max. (Inflexible); approx. 725 tons oil (each ship varied)
Coal consumption: 660 tons per day at full power
Radius of action: 6,210nm at 10 knots (oil added); 3,050nm at seagoing speed of 22.3 knots.
| Ship’s boats | Capacity |
| Pinnaces (steam): two 50ft | 140 |
| Pinnaces (sail): one 36ft | 86 |
| Launches (sail): one 42ft | 140 |
| Life cutters: two 32ft | 118 |
| Cutters: one 32ft | 59 |
| Gigs: one 30ft | 26 |
| Whalers: three 27ft | 72 |
| Dinghies: one 16ft | 10 |
| Balsa rafts: one 13ft 6in | 8 |
| Total | 659 |
Searchlights
Eight 36in, two forward superstructure abeam conning tower, two on platforms abeam fore funnel, one high on platform abeam second funnel (port), one high on platform abeam third funnel (starboard), two low down on platform on main tripod legs, one 24in signalling lamp on platform below foretop.
Anchors
Three 125cwt Wasteney Smith stockless
Two 42cwt stream and kedge (close stowing)
Two 5cwt Admiralty type.
Wireless
Mk II W/T set on completion; later changed to Types 1 and 9.
Complement
Inflexible: 779 (1910); 808 as flagship (1912)
Indomitable: