Unknown but this 15:1 gin to vermouth Martini was said to be Ernest Hemingway's favourite formula and is named after British Field Marshall Bernard Montgomery, who it is said, liked the gin in his Martini to outnumber the vermouth in roughly the same ratio as he liked to outnumber his opponents in battle.
Nicknamed ‘Monty’, Field Marshal Bernard Law Montgomery (1887-1976) fought and was seriously wounded in the First World War and was one of the most notorious British commanders in the Second World War. He commanded allied troops at the Battle of El Alamein and was a key planner of the Normandy D-Day invasion. On 4 May 1945 he took the German surrender at Luneburg Heath in northern Germany.
In chapter four of his 1951 novel Across the River and Into the Trees, Ernest Hemingway has the books main character, Colonel Richard Cantwell, order Montgomery Martinis at Harry's bar in Venice:
“Waiter,” the Colonel called; then asked, “Do you want a dry Martini, too?”
“Yes,” she said. “I'd love one.”
“Two very dry Martinis,” the Colonel said. “Montgomerys. Fifteen to one.”
“The waiter, who had been in the desert, smiled and was gone and the Colonel turned to Renata.”
“You're nice,” he said. “You're also very beautiful and lovely and I love you.”
“You always say that and I don't know what it means but I like to hear it.”
“How old are you now?”
“Nearly nineteen. Why?”
“And you don't know what it means?”
“No. Why should I? Americans always say it to you before they go away. It seems to be necessary to them. But I love you very much, too, whatever that is.”
“Let's have a fine time,” the Colonel said. “Let's not think about anything at all.”
“I would like that. I cannot think very well this time of day at any rate.”
“Here are the drinks,' the Colonel said. 'Remember not to say, chin-chin.”
“I remember that from before. I never say chin-chin, nor here's to you, nor bottoms up.”
“We just raise the glass to each other and, if you wish, we can touch the edges.”
“I wish,' she said”
The Martinis were icy cold and true Montgomerys and, after touching the edges, they felt them glow happily all through their upper bodies.