Dave, if it was from a troop ship returning from Italy, it would be No.3 Commando (one of the army commando battalions) rather than 3 Commando Brigade (who were known as 3rd Special Service Brigade in WW2.)
A good starting point would be the Commando Veterans Association (
http://www.commandoveterans.org/). After that, if you're the next of kin, you can ask the National Archives to send you his service records which will give you all the information on his time in the army.
Hopefully this was of some use and good luck with your search.
