HSC-21 Helicopter Sea Combat Squadron Two One, also known as the Blackjacks, are a United States Navy helicopter squadron based at Naval Air Station North Island. HSC-21 is made up of five expeditionary detachments that deploy aboard ships including Combat Logistics Force support ships and Amphibious Assault ships, among others, and shore base as a part of the 2515th Naval Air Ambulance Detachment, Udari Army Airfield, Kuwait. HSC-21 flies the MH-60S "Knighthawk" helicopter.