The Collaborative International Dictionary of English v.0.48:

Iwo \Iwo\ prop. n.
   a bloody and prolonged military operation in which American
   marines landed and defeated Japanese defenders (February and
   March 1945).

   Syn: Iwo Jima, invasion of Iwo.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Iwo
    n 1: a bloody and prolonged operation on the island of Iwo Jima
         in which American marines landed and defeated Japanese
         defenders (February and March 1945) [syn: Iwo, Iwo
         Jima, invasion of Iwo]