After some major redesign works, the first improved Type 039A submarine (No.321) entered service in April 2001, followed by the second (No.322) in Dec 2001. .Since then more boats have been entered service with the PLA Navy. Elimination of the stepped design for conning tower is the primary visual cue for identification of 039A variant. A new coat of anechoic tile has been applied to further reduce the noise. Compared with Type 039, the underwater performance and noise level of type 039A submarine was more satisfactory.