The first two development projects took place over a relatively short period of time, with the the first order for the PS-1 received in 1966 and that for the US-1 in 1973. However, it was not until 1996 - more than 20 years after the development of the US-1 began - that the decision to develop the US-1A Kai (later renamed as the US-2) was made. Following the notice that ShinMaywa was to be nominated as a prime contractor in October 1996, the US-1A Modification Engineering Team (USMET) was formed with cooperation from Kawasaki Heavy Industries, Ltd., NIPPI Corporation, and Mitsubishi Heavy Industries, Ltd., thereby kicking off the development efforts. With some 1,500 Japanese manufacturers participating, the entire aircraft-related industry of Japan united as one to pursue this massive project.
Although the team was supposed to “modify the US-1A,” the project was virtually no different from developing a brand new model, as they imposed three stringent engineering requirements: improved flight control during takeoff and landing on water; improved environment for patients during transport; and enhanced open sea search and rescue capabilities.
Because the primary mission of search and rescue amphibians is to save lives while landing on rough seas, meeting the requirement for landing weight was absolutely essential, and weight reduction posed the greatest difficulty for the development team. And so, the team made backbreaking efforts to reduce the weight of every single part gram by gram until they reached the target reduction. Their hard work resulted in the maximum takeoff / landing weight of 43.0 tons, which was somewhat lighter than the target. With the completion of overall assembly of the prototype No. 1 in April 2003, a rollout ceremony was conducted. In December of the same year, the first flight test was successfully conducted.
About eight years after development was commenced, the prototypes No. 1 and No. 2 were delivered to the Defense Agency in March and December 2004, respectively. After engineering and service tests by the Agency, the US-1A Kai was renamed as the US-2 STOL Search and Rescue Amphibian, and was officially deployed to a squadron in March 2007 following the Defense Minister's approval of its use by the squadron.