"the PM6 or Pilot Model Mk6 was the original troop trial version of the MK6 helmet. There were 1500 made and each one is individually numbered. There were 300 of them fitted with IS visors ... ...during 1978 limited trials were made of PM 6 including visor attachment for Internal Security use. Larger trials were planned in 1979 and quantities fixed at 1500 of which 300 were to have Internal Security visors. Contracts were placed during the same year and major trials were undertaken during July 1981. In November 1982, the PM 6 was accepted subject to the modification of the chin strap to a three point pattern and the helmet designated GS Mk.6. Contracts for pilot production of the GS Mk6 were placed during 1983 with six manufacturers each to supply 1000 helmets. Monitored issue of the GS Mk6 was undertaken by 5th Airborne Brigade during Exercise 'Lionheart'. contracts for the IS visors and kit were placed during January 1985."