[9] He had been found medically unfit "on account of small, flat chest, slight lateral curvature of the spine and defective vision", but was allowed to join so as not to disappoint the Queen.

[16] From June to September 1870 he took leave in Germany, coinciding with the Franco-Prussian war,[17] but he spent the next three-and-a-half years in the Americas (Bermuda and Halifax, Nova Scotia), where his tour of duty served to make up for the training he had missed while posted with the Prince of Wales on the Ariadne.

[18] Returning to Europe in early 1874, he was placed on the books of HMS Excellent at Portsmouth,[19] and passed the sub-lieutenant's examinations—gaining the best marks ever recorded at seamanship and joint best-ever at gunnery.

He did not enjoy the position, as the Duke was rather touchy[25] and Louis's cabin was infested with rats, one of which he caught with his bare hands as it ran across his chest as he lay in bed.

[30] Seven months after Louis left Britain on the voyage, actress Lillie Langtry allegedly bore him an illegitimate daughter, Jeanne Marie.

[31][32][33] From South Africa the Inconstant sailed to St Helena, and the Cape Verde Islands, where the squadron received orders to proceed to Gibraltar, and from there to Malta and Egypt to take part in the Anglo-Egyptian War.

[34] On 11 July 1882, Alexandria was bombarded and in the next two weeks Louis served in the Flying Squadron delivering shells and ammunition to the battle fleet, and then as a guard to the Khedive at Ras Al Teen Palace.

[36] In November 1882, he left the Inconstant, spent Christmas in Darmstadt, and in March the following year visited his younger brother, Prince Alexander, in Bulgaria.

[31] Traditionally, there was a great deal of friction between the two services, but Louis exercised his social skills in the role, leading Prince George, Duke of Cambridge, to write to him, "You have produced a mutual feeling of goodwill and unanimity which I have always wished to see established, and which, by your tact and sound judgement, you have brought about to the fullest extent.

[54] He used his relationships with the royal houses of Europe to gather intelligence on the naval fleets of other nations, which he passed on to the Admiralty in full and detailed reports.

[59] When the Second-in-Command of the Mediterranean Fleet, Rear-Admiral Burges Watson, died suddenly in late September 1902, Louis was temporarily appointed 2nd class Commodore with added responsibilities.

[60] In November of the same year he was appointed as Director of Naval Intelligence,[61][62] an apt posting for a man whom First Lord of the Admiralty the Earl of Selborne described as "the cleverest sailor I have met yet".

[64] He was promoted to rear admiral on 1 July 1904,[65] in which year his family connections to the royal courts of Europe helped resolve the Dogger Bank incident peacefully.

During a successful two years the squadron visited Greece, Portugal, Canada, and the United States, where the American press commented favourably on Prince Louis's courtesy, unassuming manner and democratic nature.

[52][66] After two years at the head of the Second Cruiser Squadron, and further visits to Spain (where his niece Victoria Eugenie of Battenberg was Queen), he was appointed second-in-command of the Mediterranean Fleet as acting vice-admiral with HMS Venerable as his flagship.

"[69] In 1909, he published a translation of Commander Vladimir Semenoff's Rasplata (The Reckoning), a memoir of the Russo-Japanese War of 1904–05, and witnessed the first crossing of the English Channel by air by Louis Blériot.

The years immediately preceding this appointment were marred by disagreements between Admirals Sir John Fisher and Lord Charles Beresford over the direction of the navy and the imposition of reforms.

[71] Fisher recommended Louis as First Sea Lord in 1911: "He is the most capable administrator in the Admirals List by a long way",[72] but elements of the British press were against his appointment on the grounds that he was a German.

The combination of frequent change and weak appointees [Wilson, Bridgeman and Battenberg] ensured that the professional leadership of the Royal Navy lost its direction in the four years preceding the war.

[78] On the eve of the World War, Churchill and Battenberg made the crucial decision to cancel the scheduled dispersal of the British fleet following practice manoeuvres, to preserve the Royal Navy's battle readiness.

[82] Anti-German sentiment rose among the British public, in newspapers, and in elite gentlemen's clubs, where resentment was inflamed by Admiral Lord Charles Beresford despite Churchill's remonstrances.

"[85] On 13 November he wrote to Churchill's Naval Secretary, Rear-Admiral Horace Hood, "It was an awful wrench, but I had no choice from the moment it was made clear to me that the Government did not feel themselves strong enough to support me by some public pronouncement".

[31] Labour party politician and trade union leader J. H. Thomas wrote to The Times: "I desire to express my extreme regret at the announcement that Prince Louis of Battenberg has, by his resignation, pandered to the most mean and contemptible slander I have ever known ...

[92] His naval career had been characterised by industry, invention and intellect; he introduced mechanical calculators to compute navigations and a cone signalling apparatus.

[31] Although assured that he would be returned to command post-war, on 9 December 1918 the First Sea Lord, Admiral Sir Rosslyn Wemyss, wrote to Prince Louis informing him that he would not be employed again and suggested that he might retire in order to facilitate the promotion of younger officers.

At the behest of the King, Louis relinquished the title Prince of Battenberg in the Grand Duchy of Hesse, along with the style of Serene Highness, on 14 July 1917.

After anglicising his surname to Mountbatten and becoming Marquess of Milford Haven, Louis wrote in his son's guestbook, "Arrived Prince Hyde, Departed Lord Jekyll".

Eventually, in January 1921, after a long and convoluted journey, the body of Grand Duchess Elizabeth Fyodorovna was interred in Jerusalem in the presence of Milford Haven and his wife.

[94] A few days later he joined HMS Repulse, the ship on which his son Louis was serving, for a week at the invitation of the captain Dudley Pound.

[105] It was his last voyage; he died at 42 Half Moon Street, Piccadilly, London in the annexe of the Naval and Military Club on 11 September 1921 of heart failure following influenza.