Fill a highball glass with ice.
Add the ginger beer to the glass.
Layer the dark rum on top of the ginger beer and give it a swirl.
Garnish with a lime ledge.
The original Dark 'n' Stormy was made with Gosling Black Seal rum and Barritt's Ginger Beer, but after the partnership between the two failed and the companies parted ways, Gosling Brothers created its own ginger beer.
Gosling Brothers claims that the drink was invented in Bermuda just after World War I.
In the United States, "Dark 'n' Stormy" has been a registered trademark of Gosling Brothers Ltd of Bermuda since 1991. Gosling's markets the drink through tie-ins to the sailing and sail racing community.
Gosling Brothers uses this registration to prohibit US marketing of a drink under the name "Dark 'N Stormy", or a related, confusing name, unless it is made with Gosling Black Seal rum.