The marine armor is one of the best armors in Fallout 76 for the late game. With that being said, the armor is hard to come by unless you know how to craft it. The problem with crafting the armor is that the plans are hard to come by. Luckily, there is a nice trick to get the plans in a pretty efficient manner.
Marine armor plans location
To get the plans, you will first want to travel to Harper’s Ferry. You will most likely discover this area while traveling across the wasteland. In case you haven’t, Harper’s Ferry can be found on the eastern side of the map in the Mire. When you fast travel to this location, you should appear in front of the building in the image below.
You will recognize the house by the large hole in the front of it. Once inside, you will notice a bunch of display cases. There are a large number of them throughout the entire house. With three floors, there are easily over 10 display cases to check. Take a look at the image below to know what the display cases look like.
The plans for the marine armor can spawn in any of these cases. Check them all, quit the game, and then load into a new server. Keep server hopping until you have all the plans. Sometimes you will get the same plans. If that happens, you can always sell them for some extra Caps or give them to a friend. If you want to expand your search, you can check the nearby vendor bot. Occasionally the vendor will have the plans.