When gunpowder goes bang the ’proof’ of the alcohol strength is at least 100 proof (114 US proof) or 57% alcohol by volume. The gunpowder was used as the test for ’proving’ there was the expected level of alcohol in the clear liquid. Plymouth Gin Navy Strength first went to sea in 1793 with the Royal Navy. The Royal Navy Supply Offices ’Pussers’ needed to check what they were buying was what they had ordered. The Pussers would use gunpowder.