General Sir Brent Spencer GCB (1760 – 29 December 1828) was an officer in the British Army during the American Revolutionary War and French Revolutionary Wars. During the Peninsular War he became Lord Arthur Wellesley’s second-in-command on two occasions. He fought at Vimeiro and testified in Wellesley’s favor at the inquiry following the Convention of Cintra. He led a division at Bussaco and two divisions at Fuentes de Onoro. After the latter action, he had an independent command in northern Portugal. Wellesley, now Lord Wellington, was not satisfied that Spencer was up to the responsibilities of second-in-command and he was replaced by Thomas Graham. Miffed, Spencer left Portugal and never returned. He became a full general in 1825.
Spencer became a commissioned officer in 1778. He fought with great credit in the West Indies in 1779–1782 during the American Revolutionary War and again in 1790–1794 during the War of the First Coalition. Promoted to brigadier general, he participated in the unsuccessful 1797 Santo Domingo campaign against Toussaint Louverture. In 1799, he led the 40th Foot during the Anglo-Russian invasion of Holland. This campaign included the battles of Bergen and Castricum.
In 1801, Spencer served with General Sir Ralph Abercromby’s army in Egypt at the Battle of Alexandria. He fought in the Copenhagen campaign in late 1807.
The Dos de Mayo Uprising of Spain against Napoleon found Spencer in command at Gibraltar. On his own initiative he sailed for Portugal and arrived at Mondego Bay on 5 August 1808. The force that he brought with him were 946 men of the 6th Foot, 806 soldiers of the 29th Foot, 874 troops of the 32nd Foot, 948 men of the 50th Foot, 929 soldiers of the 82nd Foot, and 245 artillerists. All infantry units consisted of 1st Battalions, except the 29th which was not organized into battalions. At Mondego Bay he joined his force to the 8,123 troops that Lord Arthur Wellesley brought from Cork in Ireland.
At the Battle of Vimeiro in 1808, Spencer was Wellesley’s second-in-command. He was made a Knight Companion of the Order of the Bath on 26 April 1809. He commanded the 1st Division at the Battle of Bussaco and in the 1810-1811 French invasion of Portugal. At the Battle of Fuentes de Onoro in 1811, Spencer, now a lieutenant-general, temporarily led both the 1st and 3rd Divisions.
After Fuentes, Wellington went south to participate in the Siege of Badajoz. He left Spencer and 28,000 Anglo-Portuguese to defend the province of Beira in the north.
Later that year, he was replaced by Thomas Graham, 1st Baron Lynedoch because of pessimistic letters which he had sent back to England. In 1825, Spencer was promoted to full general.
Wellington wrote of Spencer, “He was exceedingly puzzle headed. He would talk of the Thames for the Tagus.”