Cheerio! A Book of Punches and Cocktails by Charles (1928, p.17)

0.5 partOld Tom gin — Tom ginbase
1 oliveOlive — green olivegarnish
0.5 partItalian vermouth — French if preferred dry.modifier
ice — Fill with ice.other
  1. Combine the Tom gin, vermouth, and ice in a shaker.
  2. Shake, serve with a green olive, and strain into a glass.

Garnish: Green olive

Ice: Ice

See also: Martini Cocktail, Pearl Cocktail

Source allows French vermouth if preferred dry.