HMS Colossus was laid down in Portsmouth on 6 June 1879, and launched on 21 May 1882 taking three years to build. The design was by Nathaniel Barnaby, the Director of Naval Construction at the time. She is 325 ft long, 68 ft wide and has a mean draught of 26 ft. Normal displacement is 9,150 tons, of which hull and armour accounts for 6,150 tons.
Colossus represents a number of firsts in British naval shipbuilding:
The first in which steel was used for general construction (hull of open hearth steel)
The first to have compound armour generally in place of iron
The first British battle ship to carry breech loading main guns (of the new design)
Colossus, with her sister ship Edinburgh and the coastal battleship Conqueror are also the last of the citadel design ships 
Although launched in 1882, Colossus was completed 31 Oct 86. Most of delay was waiting for new guns, which were manufactured at the Government’s Woolwich Arsenal using a combination of steel and wrought iron. The 12 inch Mk II guns were not a success (one burst during trials in Collingwood), and the captain of Colossus was instructed on the first cruise not to fire the guns. The Mk II guns were replaced by an all-steel Mk IV.
Colossus was eventually armed with four 12 inch Rifled breech-Loading (RBL) guns of 25 calibres in two turrets protected by a central armoured citadel. Each gun fires a shell of 714 lb., with a muzzle velocity of 1,914 ft/sec which can pierce 20.4 inches of wrought iron at 1,000 yards. The full (battering) charge is 295 lbs. of Prismatic Brown powder.
She is also fitted with two 14 inch torpedo tubes amidships, within the armoured citadel’s protection.
Colossus took over seven years to complete, running speed trials in January 1884 and gun trials in July 1885. Commissioned at Portsmouth 13 April 1886 for Particular Service and in August joined the Channel fleet for tests. Detached for Special Duties in October and then being formally completed was sent to the Mediterranean in April 1887 where she remained for six and a half years, returning to take up duty as coastguard ship at Holyhead in November 1893. Eight years later in 1901 was paid off and passed into Fleet Reserve at Portsmouth; transferred to Dockyard Reserve in 1902 but in January 1904 was given a fresh lease of life as tender to HMS Excellent with duty as guardship at Cowes in August 1904. Ordered to be sold in September 1906 and towed away for breaking in 1908. 
Sister ship, HMS Edinburgh was used as a target for experimental firing in 1908. She was fitted with modern armour plates fully supported, for testing hits at oblique angles with filled armour piercing (A.P.) shell as supplied for war use. As a result of these trials the Controller of the Navy (Jellicoe) instructed the Director of Naval Ordnance in October 1908 to produce designs for an A.P. 12-in shell and above that would pierce thick armour at oblique impact in a fit state for bursting. Jellicoe then hoisted his flag as C.O. of the Atlantic fleet, but due to technical blunders in his absence this instruction was not carried out. This was to have profound impact on the effectiveness of British shells at Jutland.
The armoured Citadel has 18” compound armour on the beams reducing to 14” on the internal bulkheads. Turrets have 16” of compound armour on the face, reducing to 14” at the sides. The conning tower has 14 inch compound armour. The deck above the gun deck is made from 3 inch armour plating, while the armoured deck above the magazines and shell rooms is also 3 inches thick.
Teak backing was between 22” and 10”. the total weight of armour total 2,414 tons
Colossus is a ‘passable’ sea boat, having a high metacentric height (9 foot) which gives a quick and deep roll of about 9 seconds side to side.
2 sets of inverted direct compound engines by Maudsley. IHP [Indicated horse power – a measure of power used of reciprocating steam engines] 7,488 giving 16.5 knots per hour[*]
HP cylinder 58”, 2 x LP cylinders 74” dia, stroke 39”[picture]. The engines were fitted with Surface condensers.
There are 8 main and 2 auxiliary elliptical boilers working at a pressure of 64 pounds on the square inch.
Propulsion is through twin screws, 4 bladed of 17’8” diameter .
She carries five 6 inch RBLs: two broadside in the forward superstructure, two in the aft superstructure and one at the stern in a rotating mount.
(c) Rob.b1904 2008
[*] In the 1880s and 1890s the term 'Knot' was a unit of distance equal to 1 nautical mile. Charts might show distances, for example between coaling stations, as a number of knots, and the endurance of a ship could likewise be expressed as a number of knots. Speed, therefore, is expressed in Knots per Hour. However, during this period, it was also common to shorten Knots per Hour to simply Knots, and it was left to the context of use to determine whether it referred to a distance or speed. In the 20th Century, Knots invariably means a speed in nautical miles per hour