The Battenberg course indicator is a mechanical calculating device invented by Prince Louis of Battenberg in 1892 for taking station on other vessels whose range & bearing and course & speed are known. By extension, it has a range of other functions related to relative velocity calculations. A number of versions of the device were produced and it proved particularly useful for station keeping, such as ships moving in convoy during World War II. Manufacture of the instruments was contracted to Elliott Brothers, London. Devices based on the Battenberg indicator were also developed for determining course and distance in aviation and when making allowances for aircraft drift due to winds. Instruments were also manufactured for other navies, for example in the USA.