The Efficiency Decoration, post-nominal letters TD for recipients serving in the Territorial Army of the United Kingdom or ED for those serving in the Auxiliary Military Forces, was instituted in 1930 for award to part-time officers after twenty years of service as an efficient and thoroughly capable officer.

[13][14] The Efficiency Decoration was instituted by Royal Warrant on 23 September 1930 as a long service award for part-time officers of the Territorial Army of the United Kingdom and of the Auxiliary Military Forces of the British Dominions, Colonies and Protectorates and India.

[1][2] The decoration bore a subsidiary title to denote whether the recipient qualified for its award while serving in the Territorial Army or in one of the other Auxiliary Military Forces of the Empire.

[15] The decoration could be awarded to part-time officers after twenty years of commissioned service, not necessarily continuous, as an efficient and thoroughly capable officer on the active list of the Territorial Army or of any other Auxiliary Military Force of the British Empire.

[15] Recipients serving in the Territorial Army of the United Kingdom are entitled to use the post-nominal letters TD, while recipients serving in the Auxiliary Military Forces are entitled to use the post-nominal letters ED.

[8][14][15][20][21] At the same time, a clasp was instituted which could be awarded upon the completion of each further period of six years of qualifying service.

[22] In the order of wear prescribed by the British Central Chancery of the Orders of Knighthood, the Efficiency Decoration takes precedence after the Ceylon Armed Services Long Service Medal and before the Territorial Efficiency Medal.

[23] The decoration is an oval skeletal design and was struck in silver, with parts of the obverse in silver-gilt.

[24] The subsequent King George V, King George VI and Queen Elizabeth II versions are of a new design, 54 millimetres (2.13 inches) high and 37 millimetres (1.46 inches) wide, with a 15 millimetres (0.59 inches) diameter ring suspender, formed of silver wire, which passes through a small ring affixed to the top back of the crown.