It probably isn't a neat fit under any of the higher level categories, not military, not strictly migration, although many stayed. Many who came to Australia on the "Dunera" were Jewish refugees/migrants to UK from Germany categorised as "enemy aliens", but some were legitimately enemy civilians as well (e.g. interned German merchant sailors).
Category scope would need to be clear in the name - the "Dunera" served for many years in many roles - I'm guessing you would be wanting the category to be specific to the voyage than made it famous?
Maybe best fit would be under Australia as a project?
Can I suggest adding Australia to the tags to see if anyone from Australia Project can advise?