Just throwing in this tidbit, but there are many examples of naval battles during wartime where a single ship engages, or is engaged by just one ship.
http://en.wikipedia.org/wiki/List_of_single-ship_actions#World_War_I
Broadening it a bit, in WWII Bismarck put to sea with a single escort (Prinz Eugen) on a mission to sink Allied shipping, and was quickly separated from that cruiser when the action started. I feel that even in wartime, Starfleet can and will send single ships out on particular missions of destruction, just like the examples linked above. Sure, in real life support was more than likely a few hundred miles away at any given time, but given the length of typical Trek engagements a few hours or days away at warp means nothing in the typical vastness of space...
Mark
http://en.wikipedia.org/wiki/List_of_single-ship_actions#World_War_I
Broadening it a bit, in WWII Bismarck put to sea with a single escort (Prinz Eugen) on a mission to sink Allied shipping, and was quickly separated from that cruiser when the action started. I feel that even in wartime, Starfleet can and will send single ships out on particular missions of destruction, just like the examples linked above. Sure, in real life support was more than likely a few hundred miles away at any given time, but given the length of typical Trek engagements a few hours or days away at warp means nothing in the typical vastness of space...
Mark