All of the upgrades that the Armory can perform require Gold.
Upgrading things in the Armory does not require your Villagers, so you can upgrade a building while the Armory is working.
The Armory can only perform one upgrade at a time.
You cannot upgrade the Armory while the Armory is upgrading something. You must either wait, use Diamonds, or cancel the upgrade that the Armory is performing before you can upgrade the building itself.
Similarly, an upgrade cannot be performed while the Armory is upgrading.
Initially, the Armory consists of an open blue Quonset hut with a hatch on the roof where some bullets protrude from it, a pair of wooden steps out front. Several crates of ammunition are visible to the side, as well as a motor. The motor's pistons move while the Armory is upgrading something.
At level 3, the Armory gains a ventilated roof, windows with metal coverings, as well as a stone floor with linings. The roof is much smoother, and several bullets are scattered on the ground near it.
At level 4, the Armory's vent on its roof turns into a ventilation fan.
At level 5, the Armory gains a new metal entrance with closed metal doors and a small metallic ramp.
At level 8, the Armory gains a new metal extension to its right, where several green missiles packed into a cart, apparently that of the Barrage, protrude from it. The crates of ammunition are moved towards the front of the Armory, and the base of the Armory's entrance is reinforced with steel footings. There is also a caution design found just before the metal doors.
At level 14, the Armory gains an extension to the roof where several blue portions appear on top of the original roof.
At level 21, the Armory is overhauled. The entrance appears to have changed from a metal door to metal shutters. The crates containing ammunition and Barrage missiles, as well as the motor are removed. The front is reinforced with some pins, there are two vents and two hatches on the roof of the Armory, and the side that once housed ammunition gains caution designs on its edge. When the Armory is upgrading something, the hatches open to reveal what appears to be spinning gears, and a light is visible from the opening.
At level 22, two stacks, each containing a metal grate and two blue exit tubes, are added on top of the existing vents. A conveyor belt is now added to the opening, though it is inanimate. A crate of ammunition is added outside the Armory.
In the beta version, this building was known as the Combat Academy.
When a Troop upgrade finishes while the player's Landing Craft are loaded with the said troop, several of them will get out of the Landing Craft and walk across the island and back.
There's an achievement which is called Outfitter that gives a total of 60 diamonds upon finishing 235 Armory upgrades.