Topic summary
Armed merchantmen

Extracted from the Wikipedia article Armed merchantman.
While armed merchantmen are clearly inferior to purpose-built warships, sometimes they have scored successes in combat against them. Examples include East Indiamen mimicking ships of the line and chasing off regular French warships in the Battle of Pulo Aura in 1804, and the German auxiliary cruiser Kormoran sinking the Australian light cruiser HMAS Sydney in their battle in 1941, although Kormoran was also destroyed and had to be scuttled.