The mil-spec NBC (Nuclear, Biological, Chemical) M1 Canteen Cap is used for hydration with one and two quart canteens while wearing military gas masks. They include a valved drinking cap that permits use of the tubed drinking apparatus on military gas masks for hydration when masks are being worn. The NBC mask adapter has a pressure valve fitting gasket, cover, and a coupling with a self-sealing valve. The fit is for standard military one and two quart canteens or NATO standard 28mm military canteens.