The basic HGU-55/P helmet shell incorporates what feature to aid in retention of lightweight visors?

The HGU-55/P helmet shell's design includes a leather edge roll and lens stops to effectively retain lightweight visors. The leather edge roll provides a protective boundary along the helmet's perimeter while also creating a secure surface for the visors to adhere or fit against. This design aspect not only enhances comfort but also ensures the visor stays in place during flight operations, which is crucial for visibility and safety. The lens stops further ensure that the visor is held securely and maintains its position when in use.

This combination of features is specifically tailored to the operational requirements of aircrew members, who must rely on their visual aids without worry of them detaching or shifting during flight. The attention to detail in the helmet’s construction, including materials like leather for durability and comfort, highlights its functional benefits for those wearing it in demanding environments.