Army helmet

An Army helmet is a piece of wearable headgear in Fallout 4, interestingly it is identical in appearance to the combat helmet from Fallout 3 and New Vegas. It provides a ballistic protection rating of 10 (which is the same as the combat helmet) but it does not protect against energy weapons and cannot be upgraded.

Locations
It can be sold by various traders or looted around the wasteland.