borrowed fro orielly top ten tips for tomcat
If you have a WAR file, you can deploy it by simply copying the WAR file into the directory CATALINA_BASE/webapps. The filename must end with an extension of ".war". Once Tomcat notices the file, it will (by default) unpack it into a subdirectory with the base name of the WAR file. It will then create a context in memory, just as though you had created one by editing Tomcat's server.xml file. However, any necessary defaults will be obtained from the DefaultContext element in Tomcat's server.xml filel
If that does not work maybe your server.xml does not have the defaults.