intentional collision of two ships
• (n.) The act of dashing against, or striking upon.
Al·li'sion noun [ Latin allisio , from allidere , to strike or dash against; ad + laedere to dash against.] The act of dashing against, or striking upon. « The boisterous allision of the sea. Woodward. » 
The act if striking or collision of a moving vessel against a stationary object.
the striking of one ship by another.