I forgot to mention the legalities in some territorial waters, of having armed crew or security forces. And then lo and behold, after posting that, I see another thread here about Blackwater (private military - former SEAL company) launching their own ship to run escort through certain waters. I suppose that would be more cost effective than placing teams on all your ships, and it gets around the legalities of having them in territorial waters of some countries as they just escort through international waters.
The ship won't be armed per se, but the crew will be.