Admiral of the Fleet is a rank of the British Royal Navy and other navies, which equates to the NATO rank code OF-10. The rank evolved from the ancient sailing days and the admiral distinctions used by the Royal Navy then. The British fleet was divided into three divisions and each designated a colour, that of Red, White, or Blue. Each coloured division was assigned an Admiral, who in turn had command over a Vice-Admiral and a Rear Admiral. In the 18th century, the original nine ranks began to be filled by more than one person per rank. The Admiral of the Fleet commanded the admirals of the various divisions and thus, the entirety of the British fleet. As head of the Royal Navy, this position was later given the name of First Sea Lord.