[1] The formation of the regiment was prompted by the expansion of the army as a result of the commencement of the Seven Years' War.

[2] In April 1785 the regiment embarked for the West Indies[4] and was garrisoned at Saint Vincent[5] before leaving for Gibraltar in January 1793.

[6] In early 1796 the regiment returned to the West Indies to take part in a British invasion of Saint-Domingue, where most of the troops caught fever.

[2] The 1st battalion embarked for Trincomalee in Ceylon in March 1804[9] aboard the East Indiaman Brunswick.

At Albuera the battalion suffered heavy losses: 16 of its officers and 310 of its men killed, wounded or missing.

Some 140 of them made a stand at the Mundabad Ravine, which ran along the south side of the battlefield, but were forced back with heavy losses.

An Afghan artillery officer described their end: "These men charged from the shelter of a garden and died with their faces to the enemy, fighting to the death.

[38] As part of the Cardwell Reforms of the 1870s, where single-battalion regiments were linked together to share a single depot and recruiting district in the United Kingdom, the 66th was linked with the 49th (Princess Charlotte of Wales's) (Hertfordshire) Regiment of Foot, and assigned to district no.

[34] William McGonagall wrote of the Battle of Maiwand in his poem The Last Berkshire Eleven: The Heroes of Maiwand, which includes mention of Bobbie, the regimental pet dog, who survived the battle: Dr. John H. Watson, fictional narrator of Sir Arthur Conan Doyle's Sherlock Holmes stories, was wounded while attached to the regiment at the 1880 Battle of Maiwand.