US Space Shuttle crews on operational flights (STS-5 through Mission 51-L) wore no special protective pressure garments. Instead, regulation NASA blue flight coveralls were worn with the NASA LEH helmet (NASA designation LEH was given to the military AOH-1, an integrated oxygen helmet combination termed the Assembly Oxygen Helmet-1). The NASA LEH (Launch Entry Helmet) was a virtually unmodified US Navy HGU-20/P visored flight helmet that was donned via a unique "clam-shell" hinging mechanism that divided the helmet into joinable fore and aft, semi-hemispherical sections. It featured a discrete oronasal area (face seal) with a sealable, sliding face visor. This was the type of helmet assembly which was worn by the crew of the ill-fated Challenger space shuttle in 1986 and the crews which preceded them from the 5th STS flight through Mission 51-L.
The original HGU-20/P helmet had been developed by the US Navy from the USAF HGU-15/P helmet issued for use by interceptor aircrews, but had been discontinued in use after the faceplate-visor was found to severely limit peripheral vision in tactical combat situations. The helmet provided emergency oxygen in the manner of a standard pressure-demand oxygen mask, as well as crash and smoke protection, and had the appearance of a full pressure helmet, although it was not. Subsequent to the US Navy's decision to phase the integrated oxygen helmet out, the design was somewhat later revived in an adopted form by NASA for use on the early operational shuttle missions.