Singapore Sling: Achilles' Head cheat:
Note: This trick requires the entrenching tool from the Search For Yamashita's Gold mission. In the small staircase room that leads to a small indoor platform with a broken window and a catwalk leading to the industrial building (where the
first POW is found), there is a silver air duct vent on the floor by the foot of the stairs. Press Action by it and the duct will disappear, unlocking the cheat.