U-555, known as Death Avenge (デスエベンジ Desu Ebenji?) in Japan, is the sub-boss of Duff McWhalen's stage in Mega Man X5. It is a giant, whale Mechaniloid that once belonged to the marine museum and was affected by the Sigma Virus. It will pursue the player throughout the stage three times, each time attacking with a different parts of its body. First with its head, which releases Dejira GR's and fires lasers from its mouth, then with its tail (that is equipped with four missile launchers), and finally the upper body, where its core is located.