'Hypo' helmet respirator : British Army

'Hypo' or 'Smoke' helmet respirator as issued to British Army troops in summer 1915. The helmet is a simple bag made of unlined grey woollen flannel fabric, widening at the bottom where it reaches the wearer's shoulders. The single rectangular window, apparently made of cellulose acetate, is machine sewn into the front of the helmet using a strip of white cotton tape to reinforce the join. The front and rear sections of the helmet are joined by a seam which runs around the perimeter, and there is a horizontal seam located two thirds of the way down the back.

Introduced into British Army service in May 1915, the 'Hypo' or 'Smoke' helmet was intended to replace the stop-gap 'veil' respirators which had been rushed into production after the first German chlorine gas attack at Ypres in April. The new helmet was made of grey woollen Viyella or flannel fabric. It was soaked in a solution of sodium hyposulphite, (from which the name 'Hypo' was adopted) bicarbonate of soda, and glycerine, which served to keep the chemicals moist. Initially fitted with a window made of Mica, which was extremely brittle and prone to damage, later examples had windows made of celluloid, or cellulose acetate. By 6 June 1915, all British soldiers on the Western Front had been issued with a 'Hypo' helmet, but they did not prove popular in service. The troops disliked the complicated procedure for fitting (it was designed to be tucked inside the shirt and held in place by the tunic) and found it very hot and stuffy to wear. There was no valve for the intake or expiration of air, so that exhaled carbon dioxide tended to accumulate in the many folds and hollows of the fabric. It was also extremely difficult to aim a weapon while wearing it. It nevertheless represented a major improvement on the primitive 'black veil' respirator, and the 'P', 'PH' and 'PHG' helmets which succeeded the 'Hypo' later in 1915 and 1916 all followed the same basic design. Australian and New Zealand troops serving in the Anzac area were issued with 'Hypo' helmets in late 1915, in anticipation of a Turkish use of gas which did not eventuate.