Army audiences are no doubt familiar with using shipping containers as housing and other facilities on a base. Weapons systems are possible, too, for the power projection auxiliary cruiser I describe in "The AFRICOM Queen."
I recently noted a control center for unmanned surveillance craft that was housed in a shipping container.
Let me broaden this concept by going back to a post describing a Russian missile hidden in a shipping container--the Klub K (SS-N-25).
You could gather quite the Lego set of building blocks for equipping a modularized auxiliary cruiser shaped for any mission you want, on fairly short notice.