What is the origin of the idiom "son of a gun" and when to use it?

The idiom "son of a gun" has originated from the practice of allowing women to live aboard naval ships, and sometimes giving birth on board. In this context, a child born on a ship would be referred to as a "son of a gun." It is a colloquial expression that is often used in a humorous or lighthearted manner. It is typically used to playfully refer to someone, usually a male, in a slightly exaggerated or affectionate way.