A very good example of a US Army 1955 dated M-1952A Body Armour, Fragmentation Vest in a small size with side adjustment via laces.

This is the early example with shoulder straps which were delated from the pattern early on but nevertheless were issued during the Vietnam war unchanged as my last image shows

An olive drab (OD#3), one-piece design based around 12 layers of vinyl-sealed, resin-laminated, 1050 denier ballistic nylon.  It protected the torso from shoulder to waist.  It features a large, front-closing aluminium zipper and a snap-shut fly to cover it.  It has two sizable front pockets, and hangars for up to 6 grenades above them (3 over each pocket, hung by the safety lever, interestingly enough).  The vest came in three sizes – Small, Medium, and Large, weighing 6.5lb, 7.3lb, and 8.25lb, respectively.  Adjustment to the individual user could be executed with some lacing along the side – a potential gap, if it is significantly undersized for you, but an easy way to remove the vest from a casualty. The laces on this one are probably not original.

These vests remained in service through the Vietnam War, and for many years after.  Though it was officially replaced by an upgraded version in 1963, it remained in use to the end of the 1980s with some units (such as those in Berlin).  They were also in use in Ireland during The Troubles, supplementing the UK’s various body armour efforts