The S6, or Service Respirator No. 6, officially designated Respirator, NBC S6, was developed in the 1950s by the Defence Science and Technology Laboratory, Porton Down and was manufactured by the Birmingham & Leyland Rubber Company. The S6 gained notoriety when seen being used by Britain’s Special Air Service (SAS) during the widely and thoroughly documented Iranian Embassy Siege on 5 May 1980.
The features of the S6 include the very innovative inflatable air seal around the inside of the facepiece. It also had an early design of an oral-nasal cup that was built into the mould of the mask, not a separate piece extending from the interior of the facepiece to cover the nose and mouth. It features a six-point semi-elastic head harness with easily adjustable metal buckles.
A left-handed variant of the S6 was also used, with the filter being threaded onto the right-hand side of the mask. These particular models also have 'LH' (left-handed) imprinted on their rubber.
The mask provides an excellent field of vision using larger eyepieces in the shape of half-rounded rectangles.
Additionally, the S6 is made of soft black rubber. The mask uses a side-mounted filter to the left of the mask, making it much easier and more natural to shoulder a firearm for right-handed soldiers. It was very much liked by the British military for its comfort and very low breathing resistance.
Sometime around 1966, a prototype 'Extra-small' size was tested.The S6 was issued in the 58 pattern haversack originally (1966 - c.1972) before being replaced by the Mk II haversack. The original 58 pattern haversack was made of a canvas cotton blend. This presented a huge decontamination issue - the haversack could potentially soak up chemicals and the small cotton fibres were thought to be capable of trapping deposits of deployed NBC weapons. The Mk II haversack was made of nylon coated in polyurethane which was thought to make decontamination much easier.