a stone coloured variant of Service working dress is worn. Operational clothing Flying duties Aircrew-specific uniforms are officially designated as Number 14 Dress by the RAF. Aircrew on flying duties wear an olive drab flying suit in temperate regions or a khaki flight suit in desert regions. A leather flying jacket, purchased at individual expense, may be worn with the flying suit but only while the wearer is on the ground. Ground duties RAF personnel on operations, exercise or in certain tactical formed units wear Multi-Terrain Pattern (MTP) Personal Clothing System Combat Uniform (PCS CU) is a camouflage uniform. This uniform is the same as the British Army's operational uniform. This consists of PCS CU Trousers and Shirt (which is usually worn tucked in, but can be left untucked in warm climates), PCS CU smock and brown boots. A beret or 'Boonie' hat is worn as head dress. In 2006 a 45mm squared tactical recognition flash was introduced for all personnel to wear on the right shoulder of operational clothing. A small rectangular identification patch/badge such as Expeditionary Air Wing (EAW), Expeditionary Air Group (EAG), Sqn insignia or red "MP" (Military Police) badge may be worn under the TRF. A Union Flag is worn on the left shoulder. Mess dress In the RAF mess dress, officially designated Number 5 dress, is worn at formal evening functions. All regular officers, Warrant Officers and Senior NCOs possess mess dress. The current mess dress for men consists of a high waisted blue-grey single-breasted jacket fastened at the front by a single link of two RAF buttons connected by a link clip, white marcella shirt, bow tie, waistcoat or cummerbund and blue-grey trousers. Rank, for officers, is indicated in gold braid on the lower sleeve. The first RAF mess dress was introduced in 1920 and it featured a high waisted single-breasted blue-grey jacket which tapered to a point at the front below the waist. A blue-grey waistcoat, trousers and black shoes were also worn. Rank was indicated on shoulder boards in gold lace. This uniform was modified in 1928 when the shoes were replaced by boots and overalls with gold lace and bright blue stripes were introduced. This modified form of the uniform lasted until 1934 when it was replaced by a version similar to the current men's mess dress. The wearing of mess dress was suspended during World War II. For women, mess