British WWI First Pattern Hypo Helmet & Satchel

Gray shirt flannel gas hood has a single rectangular window with an amber isinglass lens.  Example is complete with the correct original rubberized fabric carrying satchel, which is faintly inscribed with a service number.  No markings are observed on the smoke helmet.  The helmet, isinglass, and carrier have some spots of discoloration but overall remain in excellent condition.  

The idea for the hypo helmet was (according to legend) suggested by a Canadian NCO.  Communicated to England on May 10, 1915, a prototype was produced that same day.  Being relatively quick and easy to produce, these were officially introduced for issue to the BEF in June 1915.  The helmet was impregnated with Hyposulphite chemicals and moistened, which neutralized the chemical agents in use at the time, and allowed the soldier wearing it to breath with relative ease.  The primary shortcoming of the early Hypo helmet was the fragile nature of the isinglass (mica) window which had to always be carefully considered when folding and handling the helmet.  $2000 - $2500