Trivia Answer: Today it is a photo-based question. What is this called, and what is the history behind it?

This sociable maritime flag is known as a “Gin Pennant” used primarily by the British Royal Navy (RN) and associated Commonwealth navies such as the Royal Australian Navy (RAN).

Flying a Gin Pennant signals the ship’s wardroom is inviting officers from other ships to come aboard and take cocktails.

Like many drinking traditions the origin of the Gin Pennant is not known, but its use has been dated back to at least the 1940′s.

Originally it was a small green triangular pennant measuring approximately 18 by 9 inches (460 by 230 mm), bearing the image of a white wine glass, nowadays the gin pennant is a Starboard pennant with a wine or cocktail glass.

According to Professor Wikipedia (of course without citation), “Its colour, size and position when hoisted were all significant as the aim was for the pennant to be as inconspicuous as possible, thereby having fewer ships sight it and subsequently accept the invitation for drinks.”

The RAN still utilizes the Gin Pennant and while in port, junior officers of one ship attempt to raise the Gin Pennant on the halyard of another ship, thereby forcing that ship to host cocktails for everyone who spies it flying.

While supposedly not an active practice in the US Navy (USN), historical accounts detail RAN officer raising the Gin Pennant on a number of units in the USN of which much camaraderie likely ensued.

Here is some information for the attached photo taken on Midway Island in 1944 where a USN unit, the USS GUNNEL, proudly displayed their Gin Pennant gifted to them by the RN (note without a glass upon it):

“Prior to leaving, officers of the Royal Navy attached to a squadron of PT boats presented Cmdr. McCain and the GUNNEL with their drinking, or gin pennant. It became a custom of the GUNNEL to fly this pennant on entering and leaving port. Their hospitality in Falmouth had been overwhelming. The bottles of gin stowed under the floorboards of the PT boats to celebrate their own victories, were the only hard liquor in town. The picture was taken on Midway Island on January 11, 1944.”

Sources:

http://en.wikipedia.org/wiki/Maritime_flag

http://www.jmlavelle.com/gunnel/patrol1.htm