The Blackfish is essentially a 10-foot long remote-controlled jet ski that is currently being tested by the navy. Its purpose is to respond to small watercrafts or swimmer who may otherwise get by undetected by the Navy’s equipment found on their bigger vessels. The Blackfish utilizes underwater sonar, surface radar and a video camera in order to monitor the waters and the surroundings, and since it can be operated up to a mile away, this should give allow the Navy sufficient time to react to any situation that may pop up.
Unfortunately (or fortunately) it does not come equipped with any sort of weapons, so I guess its purpose leans more towards surveillance rather than taking out the enemy.