Hypo-Helmet

In June 1915, 2,500,000 Hypo Helmets were issued - bags of flannel which had been chemically impregnated against chlorine. The bags were placed over the head and tucked into the collar two eyepieces cut into the front and made of celluloid enabled the wearer to peer out at the scene around him. In the autumn the British added modifications - the helmet was better impregnated and a rubber exhaust tube was added. Nine million of these P Helmets were issued by December. 

The next advance came with the introduction of the cloth helmet, impregnated as above, which had a celluloid viewing window (see Fig. 1.6). This was known as the H helmet ( H being derived from Hypo, the common name of sodium thiosulfate), and... 

Fig. 3-4. Warfare in the chemical age. (a) British soldiers at the Battle of the Somme appear to be wearing PH helmets in this photograph dated July 1916. (b) The PH helmet was an improved version of the earlier hypo and P helmets in which air was inhaled and exhaled through the fabric. The PH helmet incorporated an expiratory valve, and the cloth was impregnated with chemicals designed to destroy phosgene (the active agent was hexamethylenetetramine). This protective mask was stiflingly hot, and prolonged wear resulted in car-...

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