NATO Joint Military Symbology is the NATO standard for military map symbols. Originally published in 1986 as Allied Procedural Publication 6 (APP-6), NATO Military Symbols for Land Based Systems, the standard has evolved over the years and is currently in its fifth version (APP-6D). The symbols are designed to enhance NATO's joint interoperability by providing a standard set of common symbols. APP-6 constituted a single system of joint military symbology for land, air, space and sea-based formations and units, which can be displayed for either automated map display systems or for manual map marking. It covers all of the joint services and can be used by them. History The first basic military map symbols began to be used by western armies in the decades following the end of the Napoleonic Wars. During World War I, there was a degree of harmonisation between the British and French systems, including the adoption of the colour red for enemy forces and blue for allies; the British had previously used red for friendly troops because of the traditional red coats of British soldiers. However, the system now in use is broadly based on that devised by the US Army Corps of Engineers in 1917. The infantry symbol of a saltire in a rectangle was said to symbolise the crossed belts of an infantryman, while the single diagonal line for cavalry was said to represent the sabre belt. With the formation of NATO in 1949, the US Army system was standardized and adapted, with different shapes for friendly (blue rectangle), hostile (red diamond) and unknown (yellow quatrefoil) forces. APP-6A was promulgated in December 1999. The NATO standardization agreement that covers APP-6A is STANAG 2019 (edition 4), promulgated in December 2000. APP-6A replaced APP-6 (last version, July 1986), which had been promulgated in November 1984 (edition 3 of STANAG 2019 covered APP-6), and was replaced in turn by Joint Symbology APP-6(B) (APP-6B) in 2008 (STANAG 2019 edition 5, June 2008) and NATO Joint Military Symbology APP-6(C) (APP-6C) in 2011 (STANAG 2019 edition 6, May 2011). The U.S. is the current custodian of APP-6A, which is equivalent to MIL-STD-2525A. Symbol sets The APP-6A standard provides common operational symbology along with details on their display and plotting to ensure the compatibility, and to the greatest extent possible, the interoperability of NATO land component command, control, communications, computer, and intelligence (C4I) systems, development, operations, and training. APP-6A addresses the