A fourth ship was ordered in October 1994 with an option for two more. A fifth ship was ordered January 15, 1997. Construction began on the sixth ship in the class in 1999.
In October 1994, an order for a fourth ship was placed, with the possibility of adding two more ships later. On January 15, 1997, another ship was ordered. Construction on the sixth vessel of this class began in 1999.