Commander-in-Chief
After his return to Britain, his father George III promoted him to the rank of field marshal on 18 February 1795. On 3 April 1795, George appointed him effective Commander-in-Chief in succession to Lord Amherst although the title was not confirmed until three years later. He was also colonel of the 60th Regiment of Foot from 19 August 1797.
On appointment as Commander-in-Chief he immediately declared, reflecting on the Flanders Campaign of 1793–94, "that no officer should ever be subject to the same disadvantages under which he had laboured".
His second field command was with the army sent for the Anglo-Russian invasion of Holland in August 1799. On 7 September 1799, he was given the honorary title of Captain-General. Sir Ralph Abercromby and Admiral Sir Charles Mitchell, in charge of the vanguard, had succeeded in capturing some Dutch warships in Den Helder. However, following the Duke's arrival with the main body of the army, a number of disasters befell the allied forces, including shortage of supplies. On 17 October 1799, the Duke signed the Convention of Alkmaar, by which the allied expedition withdrew after giving up its prisoners. 1799 also saw Fort Frederick in South Africa named after him.
Frederick's military setbacks of 1799 were inevitable given his lack of experience as a field commander, the poor state of the British army at the time, and the conflicting military objectives of the protagonists. After this ineffectual campaign, Frederick was mocked, perhaps unfairly, in the rhyme "The Grand Old Duke of York":
Frederick's experience in the Dutch campaign made a strong impression on him. That campaign, and the Flanders campaign, had demonstrated the numerous weaknesses of the British army after years of neglect. Frederick as Commander-in-Chief of the British army carried through a massive programme of reform. He was the person most responsible for the reforms that created the force which served in the Peninsular War. He was also in charge of the preparations against Napoleon's planned invasion of the United Kingdom in 1803. In the opinion of Sir John Fortescue, Frederick did "more for the army than any one man has done for it in the whole of its history".
In 1801 Frederick actively supported the foundation of the Royal Military College, Sandhurst, which promoted the professional, merit-based training of future commissioned officers.
In 1801 touched by the plight of children orphaned as a result of the Napoleonic wars, Frederick issued a Royal Warrant and laid the foundation stone in Chelsea to build the Royal Military Asylum (now known as the Duke of York's Headquarters) for orphaned children. In 1892 the Royal Military Asylum was renamed the Duke of York's Royal Military School. The school relocated to Dover, Kent in 1909.
On 14 September 1805 he was given the honorary title of Warden of Windsor Forest.
Frederick resigned as Commander-in-Chief on 25 March 1809, as the result of a scandal caused by the activities of his latest mistress, Mary Anne Clarke. Clarke was accused of illicitly selling army commissions under Frederick's aegis. A select committee of the House of Commons enquired into the matter. Parliament eventually acquitted Frederick of receiving bribes by 278 votes to 196. He nevertheless resigned because of the high tally against him. Two years later, it was revealed that Clarke had received payment for furniture from Frederick's disgraced chief accuser, Gwyllym Wardle, and the Prince Regent reappointed the exonerated Frederick as Commander-in-Chief on 29 May 1811. The Duke's relationship with Mary Anne Clarke is used by Mary Anne's descendant, Daphne du Maurier, in her historical novel Mary Anne.
