Just like the 1998 version of the game, the remake of Resident Evil 2 allows players to experience the game as either Claire or Leon. Even though the majority of the game is the same, there are some changes throughout the first and second runs for each character. Thankfully, a lot of the puzzles are exactly the same, along with the method you use to unlock certain areas. This is somewhat true for unlocking the Armory, which houses a powerful pistol for Leon and the submachine gun for Claire.
Located in the S.T.A.R.S. Office, the Armory door can only be unlocked once you convince the computer that you’re a member of the team. To do this, use the S.T.A.R.S. Badge on the computer you’ll get for opening the ornate box with the scepter jewel. Once you have the S.T.A.R.S. Badge, examine the back of it to push a hidden USB stick out. You can now place it into the computer and then verify your identity to make the Armory doors open.
The earliest you can do this is after you meet Mr. X (Tyrant) for the first time in the hallway where the helicopter crashed. He will begin chasing you throughout the building, so if you’re fast enough you can run up to the S.T.A.R.S. Office and input the USB. For those not wanting to risk a potential death at the hands of this towering foe, you can come back to the RCPD as both Claire and Leon via the secret passage in the sewer’s Worker’s Break Room.
Regardless of when you decide to go for it, the only way to open up the Armory door is with the S.T.A.R.S. Badge. Additionally, you can use the badge in the Underground Stairs to open a metal display case. This can be found in the Secret Room you open via the three medallions.