British WWI Final Pattern Hypo Helmet & Satchel

Gray shirt flannel gas hood has a pair of screw-in metal bezel eye pieces with glass lenses.  Example is complete with the correct original rubberized fabric carrying satchel, which is faintly inscribed with a service number on the reverse.  No markings are observed on the helmet.  The helmet and carrier have some spots of discoloration, the eye bezels have a dark oxidized patina, and there are rust stain outlines of the eye lens bezels where it was once stored folded and the oxidation from the bezels has stained the fabric around them.  

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.  This final pattern was a significant improvement, which remained the primary issue gas defense until the new P helmets were introduced in September 1915, and then as a backup until sufficient quantities of the P helmets made it to the front lines.  $2000 - $2500