The US Department of Defense's (DoD) plans to permanently station CV-22 Osprey aircraft in Japan have been delayed by three years.

The first three aircraft were originally planned to be deployed in the fourth quarter of this fiscal year but the deployment is now expected to take place in 2020.

Reasons for the delay remain undisclosed. An additional seven aircraft are expected to arrive by 2021.

The aircraft will be permanently based at Yokota Air Base to provide increased capability for the US Special Operations forces to respond quickly to crises and contingencies in Japan and across the Asia-Pacific region, including humanitarian crises and natural disasters, the DoD stated.

The move is also expected to increase interoperability, enhance operational cooperation, and promote stronger defence relations with the Japan Self-Defense Forces.

The permanent basing of a special operations squadron of CV-22 Osprey is in line with the US commitment to defend Japan and to station its most advanced capabilities forward as part of the Asia-Pacific Rebalance.

"Reasons for the delay remain undisclosed."

The CV-22 Osprey is a tiltrotor aircraft that is equipped with integrated threat countermeasures, terrain-following radar, forward-looking infrared sensor and other advanced avionics systems.

The aircraft, which is the Special Operation Forces variant of the US Marine Corps MV-22 Osprey, can operate at low altitude in adverse weather conditions and medium to high-threat environments.

Powered by two Rolls Royce-Allison AE1107C turbo shaft engines, CV-22 Osprey can travel at speeds of 277mph.

Image: A US Air Force CV-22 Osprey. Photo: courtesy of Airwolfhound.