According to David Wondrich, this drink was "Named after an hard-hitting World War I artillery piece" and "as far as as can be determined, the only cocktail invented in the United States during Prohibition to become a classic."
Shake well with cracked ice:
1 ½ oz London dry gin
½ oz fresh-squeezed lemon juice
¾ oz simple syrup
Strain into highball glass full of cracked ice and top off with chilled champagne.
(Article is at "Celebrate Prohibition Repeal," here.)