The main armour protection for the turrets, where it rises above the level of the armoured citadel, is made from 14 inches of compound armour, thickened to 16 inches at the turret front, and backed by a layer of teak to absorb splinters.
In this view of the gun deck, we can see the mess tables for the crew, probably gunners or stokers. Ready use shells are mounted in frames around the funnel structure. These would most likely to be Palliser or armour piercing shells, and not the ‘common’ shell that carries a significant explosive charge.
Note also the black coaling hatches on port and starboard side. Coaling was a frequent and dirty evolution. Coal in hundred-weight sacks would be swung aboard from an adjacent lighter, barrowed to a deck hatch, and poured in. If the upper deck hatches were above the gun deck hatches one would imagine there would be canvas trunks to direct the falling coal, otherwise coal would form piles on the gun deck and have to be shovelled and barrowed to the nearest bunker hatch. Very messy indeed, especially as a number of the crew lived in this space. There is also a risk of the coal dust jamming the moving parts of the turret and reloading equipment.
Both turrets now have the armoured roof with the three viewing ports and sights. The central port is occupied by the Captain of the Turret, and the gun Number 1s look out from the left and right ports. Tangent sights  are mounted just in front of each port.
The roof of the turret is ventilated by a series of T frames to allow smoke to escape after firing. In practice, smoke from the guns usually dissipates well before the breeches are opened because of the time taken to train to the loading position.
Access to the turrets appears to be via the turret roof . Ladders let down from the flying deck bridging the space between the two main superstructures, or possibly rungs welded to the turret itself to allow access from the upper deck
Above the armoured citadel and gun deck is a three inch armoured deck, but this does not extend beyond the citadel. An armoured glacis ring surrounds each turret to prevent glancing shot from penetrating the gap between the upper deck and turret side.
Colossus has a low freeboard – the upper deck is only 9 ft above the water line, and thus it is likely that large seas would sweep the upper deck. To prevent (or minimise) the ingress of water through the gap between the upper deck glacis rung and the turret, flexible (canvas) covers are fitted. Part of the drill for bring the guns to the ready state includes unfastening these covers so that the turret can revolve without damaging them.
A profile of Colossus. The bridges between the superstructure are used for access in rough weather, for accessing the guns via ladders from the bridge. Anti torpedo boat guns (e.g. Nordenfelt) are mounted in the blisters around the funnel and also in the fighting tops on each mast.
The extensions in the middle of each bridge are the torpedo director positions.
(c) Rob.b1904 2008