Randomly remembered watching a Military Channel series circa 2005-2007. The episode was about a German naval armed merchant raider disguised as a Norwegian whaling ship that finally met its end after engaging at least one British warship IVO Antarctic. A shot in the dark, but does anyone else remember this episode? The only things I could find is a link about the Kormoran (which I don't believe the episode was about), and a historical document that discusses arming German whaling ships.

https://en.wikipedia.org/wiki/German_auxiliary_cruiser_Kormoran
https://www.history.navy.mil/research/library/online-reading-room/title-list-alphabetically/b/battle-instructions-for-the-german-navy.html

There was a b/w van Heflin flick, Under Ten Flags, about the KMS hilfskreuzer (aux cruiser) Atlantis.

War film footage taken about the Atlantis, starts at 12:09



I've read all the books and the Kormorman was remarkable in that she took an Australian light cruiser Sydney with her.  There were no suvivors from the HMAS Sydney.  A fire started by the Sydney could not be extinguished and the Kormorman had to be scuttled.

There are several books about those ships too and the tradition of disguised merchantmen goes back for centuries.  Modernly the Kaiser's navy preceded the Kriegsmarine and they had numerous disguised merchant raiders.  The Japanese tried the same in WW II, but it didn't work out too well for them.

Perhaps the most remarkable duel was between the US Liberty Ship Stephen Hopkins which was in a mutually fatal combat with the KMS Stier.  Both ships sank but a lot of credit should go to the US Naval Armed guard that manned the 5" gun on the Stephen Hopkins.  The Stier sank two hours after the Hopkins did.

In WW I the RN/British also operated Q ships which were merchant vessels loaded with guns and meant to entice a U-boat to the surface. They were then to lower their disguise and shell the snot out of the U-boat.  Here's a Vivien Leigh flick, Dark Journey, that has a depiction of a Q ship taking on a U-boat.  

The Germans used a dozen or so merchant raiders in WW2 with modest success.  Mostly an early war mission, I don't think any sailed after 42.  Tied down a lot of resources that could have been better utilized elsewhere.  Germans used them in WW1 as well.