Army helmet

An Army helmet is a piece of wearable headgear in Fallout 4, 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
One can always be found near a dead soldier located outside of a small trailer found en route from Sanctuary to Ranger Cabin. The trailer is located along a small body of water and is easy to locate due to the Glowing Fungus growing outside. It is recommended to travel at dark as the Glowing Fungus is more visible and the cover of night will provide easier sneak attempts against the tougher Bloodbugs, Bloatflies, and Mongrels inhabiting the area who will likely kill the sole survivor if they are attempting this at early levels. (The Army Helmet offers superior DT at the beginning of the game and will likely surpass every other equipment slot combined that the sole survivor might find for their first few levels. It is strongly recommended to take advantage of this easy acquisition.)

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