gunboat

from WordNet (r) 3.0 (2006)

gunboat
    n 1: a small shallow-draft boat carrying mounted guns; used by
         costal patrols

from The Collaborative International Dictionary of English v.0.48

Gunboat \Gun"boat`\, n.
   1. (Nav.) A vessel of light draught, carrying one or more
      guns, used for operations in shallow waters.
      [1913 Webster]

   2. (Nav.) Any small naval vessel carrying mounted guns.
      [PJC]