Do you know the make or model of the body armor from US? I'm curious.
Years ago Canadian soldiers told me that a "flak jacket" is intended to stop flak or shrapnel. It isn't intended to stop a bullet from an assault riffle. So it will stop shrapnel from a grenade going off nearby, or shrapnel from a rocket attack, but won't protect you from a grenade in your lap, or a direct hit by a rocket. It's only good for the indirect stuff. You need far stronger body armour with inserts to stop a bullet.
Since 2006 the US Marine Corp uses the
Modular Tactical Vest with Small Arms Protective Insert (SAPI). The Kevlar itself will stop a 9x19mm bullet, which is a pistol round. The ceramic plate will stop a bullet from an AK-47, but it's only rated for 3 hits, then falls apart. And if a bullet misses the plate, you're screwed.