The following are known Action Replay Codes for Fortress on Nintendo Game Boy Advance (GBA).
These codes were also known as GameShark Codes and in most cases will work on both devices.

These codes are for the U.S. version of the game.

Master Code – Must Be On
81947764
e25748a3
90032455
f10ea135

Player 1: Max Score
2992c59e
ddcf12dc
9e6491e2
9a328a06
74b76646
de9ccb0f

Player 1: Score 0
55e5739b
7f68dd40
1e08d5b0
16afd1a4
01e62c65
8e969323

Player 2: Max Score
4ccf947b
48acc818
c9db6634
bd6fd266
fc56102c
4bd0e070

Player 2: Score 0
7bd4865a
ad418247
836d2caf
eea8a5ec
602e1ae8
483c7093

Stop Timer
da7e6d76
03a5d075

Press AR Button: Slow
dbba3a89
4cb74b94