Maxson's Battlecoat

Maxson's battlecoat is a unique piece of clothing in Fallout 4.

Characteristics
Maxson's battlecoat is worn by Arthur Maxson, leader of the East Coast Brotherhood of Steel, and consists of a black BOS Officer uniform underneath a heavy padded leather coat with the Brotherhood insignia displayed on the right shoulder. Its already formidable protection can be enhanced even further by upgrading it with the ballistic weave armor mod. While the coat can't be worn underneath additional armor pieces, fully upgraded it offers better protection than a full suit of heavy combat armor and weighs less. On top of that, it grants a bonus to Perception.

Various terminal entries aboard the Prydwen shed some light on the battlecoat's background and development, even mentioning its considerable weight.

Locations
The battlecoat can only be obtained under certain circumstances. Each method requires killing him and taking it from his corpse.
 * The first method is simply killing him aboard The Prydwen at any point after meeting him. Should the player join the Brotherhood and begin the final mission with them, Maxson becomes flagged as essential henceforth, thus he cannot be killed and the coat cannot be obtained.
 * The second method is joining the Institute and progressing through their final mission Airship Down. During this mission, Maxson will appear late in the battle via Vertibird. If the Vertibird is destroyed, he will fight on the ground. This is the last opportunity to obtain the battlecoat that he wears under his power armor. It should be noted that if Liberty Prime has begun its attack on the airship, there is a limited amount of time to kill Maxson and loot his corpse before the player is teleported away.
 * The third method is by siding with the Railroad. After progressing through their quest line, during Rockets' Red Glare mission, after planting the bombs, when exiting the Prydwen, Elder Maxson will be in the Command Deck, then he can be killed and his battlecoat and also the Final Judgment Gatling Laser can be obtained.