By default, WAS uses the classic JVM, the problem is that, since version 1.0, grails doesn't work with the classic JVM. So to deploy a grails application on WAS, the instance must run with the IBM technology for java VM.
To switch an instance to the IBM technology for java VM, run the following command under qshell:
/bin/enableJvm -jvm std32 -profile profile
is the WAS edition you use.
To switch all instances, you can omit the -profile profile parameter.
Once the instance is switched, you can start it and deploy your app.
The rest is WAS administration