OF-10 in the context of "Captain general of the Army"

Field marshal (FM) has been the highest rank in the British Army since 1736. A five-star rank with NATO code OF-10, it is equivalent to an Admiral of the Fleet in the Royal Navy or a Marshal of the Royal Air Force in the Royal Air Force (RAF). A Field Marshal's insignia consists of two crossed batons surrounded by yellow leaves below the Tudor Crown. Like Marshals of the Royal Air Force and Admirals of the Fleet, Field Marshals traditionally remain officers for life, though on half-pay when not in an appointment or retired. The rank has been used sporadically throughout its history, and was vacant during parts of the 18th and 19th centuries (when all former holders of the rank were deceased). After the Second World War, it became standard practice to appoint the Chief of the Imperial General Staff (later renamed Chief of the General Staff) to the rank on his last day in the post. Army officers occupying the post of Chief of the Defence Staff, the professional head of all the British Armed Forces, were usually promoted to the rank upon their appointment.

In total, 143 men have held the rank of field marshal. The majority led careers in the British Army or the colonial British Indian Army, rising through the ranks to eventually become a field marshal. Some members of the British royal family, most recently Prince Edward, Duke of Kent and Charles III, were promoted to the rank after shorter periods of service. Three British monarchs (George V, Edward VIII, and George VI) assumed the rank on their accessions to the throne, while Edward VII and Charles III were already field marshals, and two British consorts, Albert, Prince Consort and Prince Philip, Duke of Edinburgh, were appointed by their respective queens. Other ceremonial appointments were made as diplomatic gestures. Twelve foreign monarchs have held the honour, though three (Wilhelm II, German Emperor; Franz Joseph I, Emperor of Austria-Hungary; and Hirohito, Emperor of Japan) were stripped of it when their countries became enemies of Britain and its allies in the two world wars. Also awarded the rank were one Frenchman (Ferdinand Foch) and one Australian (Sir Thomas Blamey), honoured for their contributions in World War I and World War II respectively, and one South African statesman (Jan Smuts).

Admiral of the Fleet (ADMF) is a five-star naval officer rank and the highest rank of the Royal Navy, formally established in 1688. The five-star NATO rank code is OF-10, equivalent to a field marshal in the British Army or a marshal of the Royal Air Force. Apart from honorary appointments, no new admirals of the fleet have been named since 1995, and no honorary appointments have been made since 2014.