Hooyah is the war cry or battle cry used by the United States Navy SEALs, Explosive Ordnance Disposal (EOD) Teams, and Navy Deep Sea Divers. Recently, the US Navy as a whole has adopted it as a result of MCPON Rick West's regular use of the saying. West’s son, an Active Duty Navy Diver, inspired his father who saw the value of incorporating the motivational tool Navy-wide.
It is similar to the expressions Oorah in the Marine Corps and Hooah in the U.S. Army. It is used to say Ok or understood or is sometimes used to show enthusiasm. Marine's often use it in conversational tone as an alternative to mentioning widget or whatchamacallit. Recently, Air Force Civil Engineers have taken up this battle cry replacing more traditional USAF expressions.
The origin is unclear, but may be related to "Heard-Understood-Acknowledged" (HUA).
Underwater Demolition Team veteran Jesse Ventura ended his inaugural gubernatorial speech with "Hooyah."