M52B body armor
From Halopedia, the Halo wiki
The M52B Body Armour[1] is the standard issue body armor that the Marines use for protection.
Worn by UNSC Marines, the M52B Body Armour consists of armour plating over combat fatigues, and includes a number of ammunition pockets, holsters, and other features. There seem to be a number of varieties. The equipment used in the Battle of Alpha Halo was a gunmetal grey[2], while that used during the First Battle of Earth was olive green[3]. Even later, during the Second Battle of Earth, the UNSC Marine Corps uses a different type of armour altogether, though it is still labelled as M25B on containers[4]. It may be an upgrade or new variant to the prior armour, introduced due to the needs of Earth's defenders, or even a continuity retcon by Bungie. Unlike the radically more advanced MJOLNIR Armour worn by the Spartan-II soldiers, the M52B armour does not include a dynamic recharging energy shield, providing far inferior protection against directed-energy and projectile weapons.
M52B armour crates of 12 units weigh 173 lbs altogether. Assuming the weight does not include the crate, that would indicate that the M52B armour could weigh about 14.5 lbs.
