Bob Sutor points out an article on CNet in 1998: IBM plans Web application server. "IBM is jumping into the rapidly growing market for application server software." Guess it took.
Bob also cites an article from 1998 which announces IBM VisualAge for Java. VAJ (developerWorks) is the ancestor of WebSphere Studio Application Developer and Rational Application Developer.
WAS: Back When WAS and VAJ Got Started (1998)