Hitler spent decades plotting his campaign for world domination. Alwyn Collinson, 24, a recent graduate in Renaissance history from Oxford University, hatched his own plan to invade Poland in a mere five days.

On Aug. 26 Mr. Collinson was just a marketing manager at a magazine in Oxford toying with the notion of starting some kind of a real-time Twitter project that would get people’s attention — maybe something like Orson Welles’s 1938 “War of the Worlds” radio broadcast, but that wouldn’t scare them to death.

Then suddenly he hit on the idea of tweeting the biggest terrestrial war of all time, and on Aug. 31 — roughly 72 years to the hour after Hitler’s tanks moved across the frontier — the Twitter feed RealTimeWWII was under way.

Since then the dominoes have fallen quickly. The number of followers jumped to 10,000 from about 300 by mid-September, after the project was featured on the blog The Next Web. By Nov. 9, the same date in 1939 that two British spies were captured by the SS at the Dutch border town of Venlo, the total had hit 45,000. Last week Mr. Collinson had more than 140,000 followers, dwarfing the numbers for similar feeds like @ukwarcabinet (based on documents from the National Archives in Britain detailing Winston Churchill’s cabinet debates in 1941)....