In the 18th century the royal navy gave order to have a certain stock of gin on board of every seaworthy ship. Back in the day gin was used as a remedy for numerous diseases during seafaring. From time to time the navy experienced, that some distillers watered the gin down for profit maximization.

But as gin and gunpowder where often stored next to each other on board of the vessles some smart seamen developed a method to test if the gin was watered down or not. If they poured gin over the gunpowder and it still inflamed they had the proof that the gin was not watered.

The method went down in history as the gunpowder proof or navy strength proof. The gunpowder only ignited when the gin was bottled at 57,15 % ABV.