Confidence gained from being drunk.
Many's the time that I have been prompted to do some research on a phrase after hearing a "...and that's where the phrase originated" claim on a TV show. A recent example was the BBC's Countryfile programme where a gin distiller told the world that, during the Anglo-Dutch wars in the 18th century English sailors came across gin for the first time in Holland and took a liking to it" and that's where the phrase Dutch courage came from".
As is usual with such claims, that isn't the origin of the phrase, although the origin of the word gin is related and is worth a mention.
Gin is a Dutch invention and was first distilled in Holland in the 16th century. As you may know, spirits are basically flavoured alcohol and the flavouring in gin comes from juniper berries. The Dutch for 'juniper' is 'jenever', which got Anglicised to 'ginever' and then to 'gin'.
'Dutch courage' derives from the English derision of the Dutch which came about during the Anglo-Dutch wars. Indeed, if there is one race that has been singled out for linguistic brickbats from the English it is the Dutch. Much of our language was formed in the 17th/18th centuries, at the time that the Dutch were the principal adversaries of the British. We have a number of names which have had 'Dutch' added to them to form some manner of insult:
- Dutch bargain - a contract made when one is drunk.
- Dutch concert - where several tunes are played at the same time.
- Dutch feast - where the host gets drunk before the guests.
- Dutch treat - a 'treat' at which one has to pay one's own share.
- Double Dutch - nonsense.
'Dutch courage' is another example of these slurs; it just means 'confidence gained by drinking alcohol', i.e. not actual courage at all.
The expression came into use in the early 19th century (after the end of the Anglo-Dutch wars) and was most commonly used by sailors. The first example that I have found of the expression in print is this piece from the London Courier and Evening Gazette, June 1814:
NAVAL INTELLIGENCE: The next day, when La Pique's crew were to receive their daily allowance of grog, every man threw it overboard, declaring, that they did not require Dutch courage to engage a Yankee.
Whilst it was the intended slur rather than the Dutchness of gin that brought the phrase into being it may well be that, on occasions, sailors gained their sense of abandon by drinking gin - after all, sailors will drink pretty well anything.