OMG" usage can be traced back to 1917
And speaking of Churchill, one of the earliest uses—perhaps the earliest use—of "OMG" appeared in a letter to the then-member of Parliament, as The Atlantic reports. In 1917, British Navy Admiral John Arbuthnot Fisher wrote to Churchill about rumors of new titles that would soon be bestowed. "I hear that a new order of Knighthood is on the tapis," he wrote. "O.M.G. (Oh! My God!)—Shower it on the Admiralty!" OMG, indeed.