The Knifefish is an autonomous unmanned underwater vehicle (UUV) under development by General Dynamics Mission Systems and Bluefin Robotics for the United States Navy.

It is a propeller-driven minesweeping robot designed to replace the Navy's trained dolphins and sea lions after the retirement of the 50-year-old Marine Mammal Program in 2017.

In 2014, the Bluefin-21 gained widespread recognition after it was deployed to search the seafloor of the Indian Ocean for the wreckage of Malaysia Airlines Flight 370.

[6] In April 2013, General Dynamics completed its critical design review of the Knifefish, and began developing software and hardware for the operational version of the robot.

[8] The Knifefish was scheduled to begin sea trials in 2015, and to enter into active service in 2017, coinciding with the end of the Navy's Marine Mammal Program.