Red Key

[Zig]

What is used for and where on the map i can used them

[Zonk]

there are several mission points where boxes are, which you can open with the key. Bunker, Military hill down in southwest, probably also on the new isles in the north east, but i havend been there yet.

[Sparks1968]

Yes the new complex in the North Islands has one. The far building on the second floor.

[Lord-Knight Fandragon]

The keys are used on locked boxes in military bases. You open the box and have a chance for the fancy camo guns. The best source of box farming is the bunker, theres usually 3-5 boxes in there. I typically go in with just my primary and secondary equipped, since the bunker is short range, and with the 2nd primary slot open, it lets you bring out snipers you find.