Using Tomcat 8.5.4, the version supplied with the initial Web Viewer 12.1 install, the base Tomcat URL http://localhost:8080 will redirect to http://localhost:8080/CAOMWebViewer12/index.jsp.
However, after upgrading to 9.0.80 with PTF LU11651 that redirect does not work and the base Tomcat URL http://localhost:8080 loads a Tomcat Welcome page.
Web Viewer 12.1
It is possible to redirect the Tomcat default application ROOT to another application.
After comparing the 2 Web Viewer directories apache-tomcat-8.5.4\webapps\ROOT and apache-tomcat-9.0.80\webapps\ROOT, the 8.5.4 directory had an extra file WV_redirect_install.html.
After copying WV_redirect_install.html to the 9.0.80 directory apache-tomcat-9.0.80\webapps\ROOT the URL http://localhost:8080 redirected to http://localhost:8080/CAOMWebViewer12/index.jsp.
No restart of Tomcat was required but a refresh of the browser cache/restart of the browser may be needed to see the change.
After further investigation, it was found that some Web Viewer 12.1 Tomcat updates like 9.0.80 do not contain the file WV_redirect_install.html. Engineering will investigate this problem further.