Where does the term 'Son of a Gun' come from?

Answer 1

Ships

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Agreed. The gun deck of square-rigged ships became the source of this common expression. Wives of Royal Navy crewman occasionally were permitted to go on long voyages with their husbands, and - not surprisingly - some of them would become pregnant. The only safe place to give birth was behind a canvas shelter rigged up between cannons on the gun deck, so a baby born in this way was dubbed a 'Son of a gun', a term that also hinted at the identity of the father.

In any case, the term was adopted in civilian life, and it survived long after the British Admiralty outlawed the practice of wives living on board in 1840.