Meet the Enemy and Descend
If you accidentally encounter one of the roaming green trucks on the over world map you will be forced to descend and meet with the enemy. This will throw you into a sub-game that pays homage to Commando (NES). This song is played as you fight the ground enemies.
Bionic Commando (NES)
This is the original version of the song, it is track 11 in the NSF file.
The track exists in the soundtrack album, and the title comes from the message you get when you have to fight the enemy.
In the liner notes of the official 8-bit soundtrack, Dean Tersigni writes:
Bionic Commando: Rearmed (W32)
The song was completely remixed for Rearmed. It plays in the normal location, but has an alternate version for the secret tunnels.