Conceived by the First Sea Lord Admiral Sir John Arbuthnot Fisher in the same year (1905) as his revolutionary Dreadnought, the genus of the battlecruiser was actually as a commerce protection vessel rather than a conventional fighting ship. When, ten years later, the battlecruisers were called upon to reinforce the battleships of the Grand Fleet, their original designated role seems to have been forgotten and their inherent weaknesses only realised when it was too late to save three of them from oblivion. H.M.S. Lion was one of the second generation of "Jackie" Fisher's new breed of thoroughbreds which, hitherto, had been of lesser displacement than their battleship counterparts. Indeed, it was only after Lion and her sisters were completed and commissioned that the term 'battlecruiser' was first coined; up until 1913, the two earlier trios of Lion's predecessors had been classified as 'large armoured cruisers' which, with hindsight, was perhaps more appropriate.

The first of three identical sisters, Lion was built at Devonport where her keel was laid on 29th November 1909. Construction proceeded apace and she was launched on 6th August 1910 and completed in May 1912 at a final cost, including guns, of £2,086,458. Displacing 29,680 tons (fully loaded) and measuring 700 feet in length with an 88½ foot beam, she had armour-plating up to 9in. thick and her Vickers' turbine engines developed 70,000shp. to give her a maximum speed of 17 knots. Impressively armed with 8-13½in. guns, 16-4in. and 4-3pdrs., she also carried 2-21in. torpedo tubes and mustered a crew of 997 officers and men. The largest, fastest and most expensive capital ships of their day, Lion and her sisters seemed to embody the acme of progress and technology as each prepared to join the fleet in that uneasy lull before war broke out in August 1914.

Commissioned into the 1st Cruiser Squadron on 4th June 1912, she became flagship to Rear-Admiral Bayly the next month and, six months later, hoisted the flag of Rear-Admiral Sir David Beatty, in command of the 1st Battle Cruiser Squadron based at Rosyth. Like most senior officers, Beatty was elated when War was declared on 4th August 1914 and, within three weeks, his squadron was engaged off Heligoland Bight when three German cruisers and a destroyer were sunk in a textbook action. The far more serious encounter off the Dogger Bank on 24th January 1915 had a less successful outcome however, due to a mixture of Beatty's impulsiveness and a general lack of understanding of his sometimes ambiguous orders. Although the German armoured cruiser Blücher was sunk, the remainder of the German squadron escaped unscathed despite Beatty's overwhelming numerical superiority in both ships and firepower. As if to emphasis her own commander's shortcomings, Lion herself sustained several hits, including two on the waterline which, had they flooded the engineroom as very nearly occurred, would have been totally disabling. As it was, Lion had to be towed home by Indefatigable and spent the next four months undergoing repairs. Back on station by the summer of 1915, it was to be another year before she was in action again and at Jutland (31st May -- 1st June 1916), Lion was in the van of Beatty's six-ship squadron during the so-called "run to the south" that began the battle. The two rival battlecruiser fleets opened fire at 3.48pm. and only twelve minutes later, Lion received a direct hit on "Q" turret, amidships, which not only blew half of it away but also ignited the cordite in the loading cage killing everyone in the gun-house and working chamber. Smouldering charges lower down then ignited when the ship turned into the wind, killing the magazine and shell room crews, and had it not been for the gallantry of a dying Royal Marine officer (Major Harvey) who flooded the magazines in the nick of time, there is little doubt that Lion would have blown up in the same spectacular fashion as her sister Queen Mary and also Indefatigable, both of which sank with massive loss of life.

Though she was speedily repaired after Jutland, Lion saw little further action during the remainder of the War when she flew the flag of Vice-Admiral Pakenham, Beatty having replaced Jellicoe as C. in C., Grand Fleet. When peace came in November 1918, her operational career was effectively over and although she remained flagship to the 1st Battle Cruiser Squadron until 1923, her fate had already been decided by the 1922 Washington Treaty (on naval disarmament) and she was scrapped in 1924. It was a sad end for such a mighty ship, especially one which had survived two near-disasters at the hands of her German foes, but times were changing and the battlecruiser experiment had run its course.