During the 1990s, by which point the US-1A fleet was beginning to show its age, the JMSDF attempted to obtain funding towards acquiring a replacement, but could not secure enough to develop an entirely new aircraft. Therefore, during 1995, ShinMaywa (as Shin Meiwa had been renamed, reportedly so that the name would be easier to pronounce for non-Japanese speakers) set about planning to produce an upgraded version of the US-1A, initially referred to as the "US-1A "kai" "("US-1A 改" - "improved US-1A"). This aircraft features numerous aerodynamic refinements and modernised systems, along with a pressurised hull, and the adoption of more powerful Rolls-Royce AE 2100 engines. Flight tests of the new variant began on December 18, 2003. The JMSDF has chosen to purchase up to 14 of these aircraft, which has entered service as the ShinMaywa US-2.