The U-3 was one of the experimental bio-weapons developed by Osmund Saddler's research team on the island. It was a horrifying chimera of human, insect, and reptile DNA fused imperfectly into a single being, itself hosting a Plaga parasite.[excerpt 1]
Saddler first mentioned the U-3 to Leon after the battle with Krauser, calling the creature "It". Later, in the underground cellars, the U-3 bursts out from a wall, causing Leon to jump out of the way, into a suspended set of crate rigs. The rigs repeatedly dropped into the abyss below after two switches were pushed per rig. After dropping the second crate rig, the U-3 sprouted a massive Plaga from its back. When Leon dropped the third crate rig, the U-3 fell with it. However, the U-3 continued to pursue Leon, scaling a wall of the chasm. The U-3 was severely damaged and began to burrow underground for concealment. After destroying the Plaga, the U-3 finally died.