Battleships ruled the waves - it had always been that way, it would always be that way ... If not for the rise of the aircraft - with its ability to drop bombs (against a battleship's deck armour) and its ability to launch torpedoes (against a battleship's hull form, propellers and rudder). Battleships were overhauled, with thickened deck armour (to guard against bombs), with hull form bulges (to guard against torpedoes) and with many anti-aircraft guns (to target enemy aircraft). These could come in two varieties. The first: dedicated secondary armament - that was dual purpose, being capable of targeting both air and surface targets. These guns would usually be around 4 to 5 inch calibre. Their shells either exploded at a predetermined altitude, or at a preset proximity from the enemy aircraft (in the later stages of World War Two). The second: dedicated anti-aircraft guns, which could only target aircraft. These guns would usually be around 0.5 inch to 40 mm calibre. They mostly relied upon their rate of fire - to both deter, and 'bring down' enemy aircraft.
The American 'twin barrel' 5 inch naval gun is regarded as 'one of the most successful naval guns' of all time:
Part of its success, comes from the fact that the US Navy standardised the 5 inch gun, for use on both battleships and smaller warships (such as cruisers and destroyers). This made shell logistics 'so much simpler'. On a battleship, the twin 5 inch was only ever a secondary armament (for use against aircraft and surface targets). Whilst on cruisers and destroyers, the 5 inch 'was usually' the primary armament - with up to eight turrets being installed (for example) on the 'light cruiser' USS Atlanta (which featured six centreline turrets 'for stability reasons' and two wing turrets 'for maximising' anti-aircraft firepower). The 5 inch gun was heavily used throughout World War Two, to defend the American warship fleets 'in the Pacific'. When used to defend against enemy aircraft, several turrets would operate together, using barrage fire (the idea being: not to target the enemy aircraft directly, but rather 'target the area' that the enemy aircraft was in) and destroy the aircraft with shrapnel 'exploding outwards' from the 5 inch shells (which were equipped with proximity fuses). As an anti-aircraft gun, the twin 5 inch 'more than proved its worth', and it was a gun turret that would not be easily mothballed - even after World War Two had finished (in 1945) ... When the Iowa class battleships were reactivated (in the 1980s'), the venerable twin 5 inch dual purpose gun, was retained as part of their armament - although with only six turrets (as opposed to ten turrets) to make room for newer 'more modern' missiles.
The early World War Two modifications of HMS Hood, resulted in Hood's 'boat deck' (also called her 'shelter deck') being outfitted with seven 4 inch 'twin barrelled' anti-aircraft guns:
This was something of an 'austere makeover' that aimed to increase Hood's anti-aircraft capabilities. To 'make space' for installing these guns, all of Hood's single barrelled 4 inch anti-aircraft and 5.5 inch naval guns 'were removed' - although facilities (such as their magazines and 'shell supply lines') were enhanced to support her new guns. These modifications were carried out 'more for speed' than for robustness reasons - as the entire 'boat deck' could really be considered as a target for incoming shells! This issue was further compounded, by the fact that 'ready use' ammunition lockers were installed 'next to and near' each anti-aircraft gun mount. During the Battle of the Denmark Strait, a boat deck fire 'wreaked havoc' amongst the ammunition that was stored in these.
Here we can see the details of the midships area of HMS Hood:
Of particular interest are: i) The eight barrelled 2 pounder anti-aircraft pom poms gun. ii) The 4 inch high angle anti-aircraft gun. iii) One of the secondary armament 5.5 inch naval guns (with it's protective shield). iv) The smaller crane derricks, which were helpful for lifting both ammunition, and smaller boats. v) The torpedo look out control towers. Which I believe, would issue just one command: take evasive action! vi) Venting for the boiler rooms (located at the base of the funnels, just under various life rafts). vii) The smokestacks themselves, which vented waste gases and heat, from Hood's boiler rooms. There's an unproven theory, that the shell that sunk HMS Hood, may very well have penetrated one of these, and detonated the oil fuel (inside her boiler rooms).
Here we can see the look out posts for the various crew members of HMS Hood, that were tasked with looking out for enemy aircraft:
Most of these involved some sort of optical sight (such as binoculars), whereby it's operator would locate enemy aircraft, then obtain various measurements (such as bearing and elevation), which in-turn, was fed into several (analogue) fire control computers, which in-turn was relayed to the gun operators (who opened fire). Hood's anti-aircraft guns, were also capable of local control, when (for example) such bridge tower directors had been knocked out.
From left to right we have: the aft-most eight barrelled 2 pounder anti-aircraft pom poms gun, two 4 inch high angle anti-aircraft guns, and one of the fifteen inch naval gun turrets (with it's local control range finder on-top). The anti-aircraft guns, were situated atop the Admiral's Day Cabin, and much pomp and ceremony, is often associated with the wooden handrail ladders, that lead to this area (bottom left). This was particularly true, of Hood's Empire Cruise, where she entertained VIPs (such as Royalty), from around the World.