The P (or Phenate) Helmet, officially called the Tube Helmet, appeared in July 1915, replacing the simpler Hypo Helmet. It featured two mica eyepieces instead of the single visor of its predecessor, and added an exhaust valve fed from a metal tube which the wearer held in his mouth. The exhaust valve was needed because a double layer of flannel – one treated and one not – was needed because the solution attacked the fabric. It had flannel layers of cloth-dipped in sodium phenolate and glycerin and protected against chlorine and phosgene, but not against tear gas. Around 9 million were made.