If you are having to make a UML diagram with Microsoft Visio, you might be a bit frustrated with the built in templates.
I found a website which offers a free UML 2.2 template which seems to do the job: http://www.softwarestencils.com/uml/index.html
Seems you just download the Zip file, and can then double click on the files to have them imported into Visio.
Thought it was worth sharing.