Admiral of the Fleet Alfred Ernle Montacute Chatfield, 1st Baron Chatfield, GCB, OM, KCMG, CVO, PC, DL (27 September 1873 – 15 November 1967) was a Royal Navy officer. During the First World War he was present as Sir David Beatty's Flag-Captain at the Battle of Heligoland Bight in August 1914, at the Battle of Dogger Bank in January 1915 and at the Battle of Jutland in May 1916. After the war he became Commander-in-Chief, Atlantic Fleet and then Commander-in-Chief, Mediterranean Fleet before serving as First Sea Lord in the mid-1930s in which role he won arguments that the Royal Navy should have 70 cruisers rather than the 50 cruisers that had been agreed at the Naval Conference of 1930, that the battleship still had an important role to play despite the development of the bomber and that the Fleet Air Arm should be part of the Royal Navy rather than the Royal Air Force. He subsequently served as Minister for Coordination of Defence in the early years of the Second World War.

Born the only son of Admiral Alfred John Chatfield and Louisa Chatfield (née Faulconer), Chatfield was educated at St Andrew's School in Tenby before he entered the Royal Navy as a cadet in the training ship HMS Britannia in 1886. He went to sea as a midshipman in the corvette HMS Cleopatra in November 1888 before transferring to the cruiser HMS Warspite, flagship of the Pacific Station, in 1890. Promoted to sub-lieutenant on 27 September 1892 and to lieutenant on 27 March 1894, he joined the battleship HMS Royal Sovereign, flagship of the Channel Fleet in May 1894. He attended the gunnery school HMS Excellent in 1895 and then joined the staff at the gunnery school HMS Cambridge at Devonport in August 1897. Chatfield became gunnery officer in the battleship HMS Caesar in the Mediterranean Fleet in January 1899 and then joined the staff of the gunnery school HMS Wildfire at Sheerness in January 1900 before becoming 1st lieutenant and gunnery officer in the cruiser HMS Good Hope in the Atlantic Fleet in November 1902. Promoted to commander on 1 January 1904, he transferred to the battleship HMS Venerable in the Mediterranean Fleet in January 1904.

He returned to HMS Excellent in March 1906 and, having been promoted to captain on 30 June 1909, he became Flag Captain of the battleship HMS Albemarle, flagship of Rear-Admiral Sir Colin Keppel, second-in-command of the Atlantic Fleet, in September 1909 and then Flag Captain of the battleship HMS London, Keppel's new flagship in the same role, in February 1910. After attending the War course at the Royal Naval War College at Portsmouth, he served as Captain of the converted liner RMS Medina for the Royal Tour of India in 1911 and was appointed to the Royal Victorian Order as a Commander in February 1912. He was then given command first of HMS Aboukir in the Reserve Fleet in Summer 1912, then of the cruiser HMS Southampton in September 1912 and subsequently of the battlecruiser HMS Lion, flagship of Rear-Admiral David Beatty's First Battlecruiser Squadron, in March 1913.

During the First World War Chatfield was present as Beatty's Flag-Captain in the Lion at the Battle of Heligoland Bight in August 1914, at the Battle of Dogger Bank in January 1915 and at the Battle of Jutland in May 1916. It was at Jutland, after two British battlecruisers had blown up, that Beatty made his famous remark, "There seems to be something wrong with our bloody ships today". Appointed to the Order of St Michael and St George as a Companion on 31 May 1916 and to the Order of the Bath as a Companion in the 1916 Birthday Honours, Chatfield went on to command the battleship HMS Iron Duke, Beatty's flagship as Commander-in-Chief of the Grand Fleet, in November 1916 and then the battleship HMS Queen Elizabeth, Beatty's new flagship in the same role, in February 1917. He was advanced to Knight Commander of the Order of St Michael and St George on 5 April 1919.

After the war Chatfield served as Fourth Sea Lord from July 1919 and, having been appointed Naval Aide-de-Camp to the King on 26 January 1920 and promoted to rear-admiral on 31 July 1920, he became Assistant Chief of the Naval Staff in February 1920. Chatfield attended the Washington naval conference in 1921-1922 that ended for the moment the mounting Anglo-American-Japanese naval arms race in the Asia-Pacific region. In private, Chatfield felt that the Foreign Secretary Arthur Balfour had given away too much in his talks with the Americans and the Japanese, but also felt the British "might well have done worse...We had successfully resisted efforts to limit our cruiser and destroyer numbers." Chatfield also noted that the Geddes Committee had already ruled in its report on 11 February 1922 that the Royal Navy was too expensive. The committee declared that some 35, 000 sailors were redundant and the naval budget should be cut by £21 million, which meant the Royal Navy was going to be reduced in size regardless of what the Washington conference had decided.

Advanced to Knight Commander of the Order of the Bath in the 1922 Birthday Honours, he was appointed Commander of the 3rd Light Cruiser Squadron in September 1922 and Third Sea Lord and Controller of the Navy in April 1925. As Third Sea Lord, Chatfield became keenly concerned about the British shipbuilding industry, which went into contraction as the Anglo-German naval arms race had ended and the Washington treaty imposed limits on shipbuilding. Equally worrisome to him was the increasing cost of warships owing to technological innovation, which led him to express concerns that the necessary political will to spend millions of pounds upon the Navy was being eroded.

Promoted to vice-admiral on 1 March 1926, he went on to be Commander-in-Chief, Atlantic Fleet, with his flag in the battleship HMS Nelson, in March 1929 and, having been promoted to full admiral on 1 April 1930, he became Commander-in-Chief, Mediterranean Fleet, with his flag in the battleship HMS Queen Elizabeth, in May 1930. Chatfield became First Sea Lord in January 1933 and was advanced to Knight Grand Cross of the Order of the Bath in the 1934 New Year Honours. As First Sea Lord he won arguments that the Royal Navy should have 70 cruisers rather than the 50 cruisers that had been agreed at the London Naval Conference 1930, that the battleship still had an important role to play despite the development of the bomber and that the Fleet Air Arm should be part of the Royal Navy rather than the Royal Air Force. Chatfield played a key role in fashioning tactics that favoured night fighting and less centralised manoeuvres as the basis of tactics for future fleet battles. The American historians Williamson Murray and Alan Millet wrote that the Royal Navy in the interwar period did a superb job in training admirals and captains in the style of the 18th and early 19th centuries, so that "...in the future there would be few of the egregious errors that marked the Battle of Jutland". Rear-Admiral (S) Sir Rowland Jerram who served under Chatfield for 20 years as his private secretary described him as: "an officer of the old school in upbringing, but certainly not lacking in imagination and breath of view; of the highest ability as a seaman, a leader and in the higher ranks, a debater, sure of himself and 100% trusted by the Navy". The British historian Andrew Gordon described Chatfield as a man of the "upmost integrity, humourless, very just, very aloof, very charming, very tactful, supremely efficient and an intellectual" and "quite possibly the best peacetime First Sea Lord the Admiralty ever had". Chatfield's principal concern upon becoming First Sea Lord was ensuring that the British shipbuilding industry, which had been hard hit by the Great Depression, received enough orders for warships to keep the industry going.

When Chatfield became the First Sea Lord, the Admiralty was in a weak position with regards to the Treasury. The Prime Minister, Ramsay MacDonald, was generally supportive of the Admiralty, but had been weakened by the split in the Labour Party in 1931 with McDonald leading a rump National Labour Party (which was the smallest of the parties that made up the governing coalition) in opposition to the Labour Party. The Foreign Secretary, Sir John Simon, was considered to be highly intelligent, but seemingly incapable of making a decision as Simon would lay out the options in foreign policy and then find himself unable to choose which option to pursue. The dominant personality in the cabinet was the Chancellor of the Exchequer, Neville Chamberlain, who was considered to be the most able minister in the National Government and already widely viewed as a future prime minister. With a weak foreign secretary and a prime minister leading a rump party in the coalition National government, the influence of the Treasury, which considered naval spending wasteful, was in the ascendency. The so-called "ten year rule" introduced in 1919 under which the service chiefs were to base their defence estimates on the assumption that there would be no major war in the next years had abandoned in early 1932 in response to Japan's aggression in China, but it was still unclear just how far the cabinet would go with rearmament. In response to Chamberlain vetoing a request from the Admiralty requesting more stockpiling of fuel, more reservists for the Royal Navy, and more aeroplanes for the Fleet Air Arm, Chatfield together with the other three sea lords wrote to the cabinet on 16 January 1933 that they could only accept the Treasury viewpoint on naval spending "if the cabinet is aware of and prepared to take responsibility for the continuance of these serious deficiencies". It was in part to resolve the dispute about what form British rearmament should go and in part how much to spend on rearmament that the Defence Requirements Committee was formed in November 1933. Chatfield found himself at odds with Chamberlain and the Treasury who favoured a return to the Anglo-Japanese alliance that had ended in 1922. The call from Chamberlain to a return to the Anglo-Japanese alliance prompted a strong reaction from the diplomats with Charles Orde, Robert Craigie, and Laurence Collier all writing that Japan was dead-set on an anti-Western course, and there was no hope of lasting understanding with Japan.