Heavy impact plating
From Halopedia, the Halo wiki
Heavy impact plating (also known as heavy blast armor) is a type and variation of body armor system used by UNSC soldiers and Marines. It is worn over the wearer's camouflage utility uniform, and is composed of metal segments that bulwark and protect everything vital from the neck to the knees. Impact plating is impervious to light handheld firearms such as automatic pistols.
Impact plating is usually not worn for rapid, airborne strikes, but Staff Sergeant Avery Johnson and Staff Sergeant Nolan Byrne were ordered to wear impact plating on their assault on an Insurrectionist bomb-shop on the UNSC planet Tribute.
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