Those also sound good. I'm always a fan of more espionage options. However, I still like the idea of directly controlling units that can freely attack without declaring war. It's hard to cite specific examples in contemporary history, but it feels like it would be realistic and fun. I actually tried modding my game to implement this, and it seems to work pretty well. I simply copied the relevant xml from the privateer and pasted it into the xml for the marine. You can attack units without war as expected, but you cannot attack into city tiles without war. If you are at war, you can capture cities. I'm not sure how the AI will use the units, but I will see as I continue my current playthrough.