The design for the
Buque de Proyección Estratégica (Strategic Projection Vessel), as it was initially known, was approved in September 2003. , July 2013 The vessel has a
flight deck of , with a ski-jump ramp. The ship's flight deck has eight landing spots for Harrier, F-35 Lightning II or medium-sized helicopters, four spots for heavy helicopters of the
CH-47 Chinook or
V-22 Osprey size. The ship can carry either 30 helicopters or 10/12 McDonnell Douglas AV-8B Harrier II or Lockheed Martin F-35 Lightning II and 10/12 helicopters, using the light vehicles bay as an additional storage zone. The ship uses
diesel-electric propulsion, simultaneously connecting both diesels and the new technology
gas turbine powerplant to a pair of
azimuthal pods, for the first time in the Spanish Navy. The complement of the ship is approximately 900 naval personnel, with equipment and support elements for 1,200 soldiers. Multi-functional garage and hangar space on two levels covers , with capacity for 6,000 tonnes load on each level. A stern
well deck measuring can accommodate four
LCM-1E landing craft which can beach-deliver non-swimming ground vehicles like tanks and four RHIBs, or one
Landing Craft Air Cushion plus
Assault Amphibious Vehicles. While the ship has also operated the
AV-8B Harrier II fighter aircraft, as of 2025 it was reported that the aircraft would be unlikely to be replaced given that the acquisition of the
F-35B fighter has been ruled out by the Spanish government. If confirmed, this means that carrier-based fighter operations on
Juan Carlos I will cease in around 2030. ==Construction==