Admiral Charles Napier vanquishes the navy of the Portuguese usurper Dom Miguel at the third Battle of Cape St. Vincent.

Admiral is one of the highest ranks in many navies. In the Commonwealth nations and the United States, a "full" admiral is equivalent to a "full" general in the army or the air force. Admiral is ranked above vice admiral and below admiral of the fleet, or fleet admiral.

Admiral Sir Charles John Napier was a British naval officer whose sixty years in the Royal Navy included service in the War of 1812, the Napoleonic Wars, Syrian War and the Crimean War, and a period commanding the Portuguese navy in the Liberal Wars. An innovator concerned with the development of iron ships, and an advocate of humane reform in the Royal Navy, he was also active in politics as a Liberal Member of Parliament and was probably the naval officer most widely known to the public in the early Victorian Era.

The Kingdom of Portugal was a monarchy in the western Iberian Peninsula and the predecessor of the modern Portuguese Republic. Existing to various extents between 1139 and 1910, it was also known as the Kingdom of Portugal and the Algarves after 1415, and as the United Kingdom of Portugal, Brazil and the Algarves between 1815 and 1822. The name is also often applied to the Portuguese Empire, the realm's overseas colonies.

A usurper is an illegitimate or controversial claimant to power, often but not always in a monarchy. In other words, one who takes the power of a country, city, or established region for oneself, without any formal or legal right to claim it as one's own. Usurpers can rise to power in a region by often unexpected physical force such as via a coup d'état, as well as through political influence and deceit.