Armored Core 2 - Another Age

There are 12 hidden parts. 

1) Test Arena
In the garage if you enter the test arena you will notice a panel at the very top in the middle. Blast it, it takes quite a few shots with weaker weapons. Then to make sure you get up there nice and easy just hit L2+R2+R3(analog joystick button) This will override your boost disconnect and gives you unlimited power for about 1 minute. Of course, be aware that after the minute is up you won't be able to use any energy for another minute. The part is on the ledge in the top, it's an antenna and it's a turquoise color.

2) Escort Train
I'd suggest getting the part after you complete the game and all the missions are unlocked. When the train comes in, shoot the next to last car, the part should be there, grab it! This does fail the mission though.

3) Guard Secret Information
You will need the helm with a hacking ability of 5 for this one. You will come to a room with two doors, the one on the left goes down a small hallway to a door that you normally cannot open, you will find a room with crates, destroy the group of crates in the center of the room and then destroy the grate underneath them, drop down and get the part. Ya can buzz right by the security drones in the mission.

4) Rescue Research Team (Moonlight Sword)
Drop all the way down the pit. You can jump on the disc in the tunnel and ride it to about halfway down the tunnel to the spot with the covered hole. Shoot it and drop on down. Looks in the far end in a niche in the corner.

5) Infiltrate Radar Base
Go through the maze like first part. Once ya reach the second part, outside again go to your right, you will see a large 6 room garage type deal. In one of the rooms is the part, look on the side closest to the mountain.

6) Destroy Radar Base
Same area as Infiltrate Radar Base and in the same spot.

7) Ground Based Attack
Fly to the other end of the bridge, next to the last pillar, go under the bridge and the part is sitting there on a little ledge underneath.

8) Stop Surface Weapon (Karasawa Mk2)
Fly back into one of the corners, the part is around there. You may want to start on some of the guns on the Surface weapon before you go for the part, this gives ya some more time.

9) Destroy Containers
A little tip first, you should be able to see all the containers on your map screen. You may want to destroy all the containers on top first. The part is hidden behind a piece of the aircraft in one of the ravines.

10) Underground Railway
You will come to a room with a blast able floor, before you blast it look up and you will see a blast able ceiling. Blast away and fly up. The part is at the end.

11) Zio City Suppression
What a pain this mission is. You have two of these annoying Arena opponents blasting you with their high powered weapons. The best way I found to do this is have the Karasawa or some other high powered weapon (Grenade Launcher) and get your back up to the tower quickly. Kill one as soon as ya can, and beat up the second a little. Don't destroy the second or the mission will end. You will find about 3 or 4 groups of green city mazes. In one of the green city mazes you will find the part, it's not terribly hard because it's quite a large part. It isn't by the green city maze you start next to though.

12) Eliminate Leos Kline
Once ya get passed the floating mines you will come to a hallway with two doors, in one of the doors you will see a generator part sitting there.