How the Bernoulli Equation Changed WWII
My wife and I are avid fans of Brendan Fraser, his movie “Blast From The Past” being one of our favorites. When we learned he was starring in the recent movie “Pressure” we had to see it! Just from the ads for the movie, we knew it would be about the events surrounding D-Day and the great emotional decision-making “Pressure” that General Eisenhower (Ike) was under as he coordinated this monumental military invasion. The movie was clearly all that! The first clue that something wasn’t right was that D-Day was scheduled for June 5th when we know that it was ultimately on June 6th. Why it was a different date became the theme of the movie.
The movie begins by introducing us to an RAF meteorologist, James Stagg. He is assigned to Ike’s staff several days before the scheduled invasion, having proven his meticulous, data driven approach to weather prediction. A USA Air Force meteorologist, Chris Krick, is already on Ike’s staff and has been for some time. As the movie proceeds, Stagg and Krick totally disagree with what the weather will be like on June 5th at Normandy. The basic difference is that Stagg is looking at the current data on two storms that will collide at Normandy on the 5th and Krick was looking at years of actual recorded weather conditions that had existed in years past at Normandy. History indicated that the weather would be fine on the 5th. In fact, we learn that Krick has been correct 100% of the time for all previous invasions since joining Ike’s staff. However, Stagg argues that Krick’s accuracy has been because of their particular locations. Stagg says that the decision cannot be based on history when the current data indicates otherwise. Eventually, despite Krick’s record, Ike goes with Stagg’s recommendation and postpones the invasion. From a weather standpoint, this means the next best chance for the invasion will be June 18th. No one on Ike’s staff is happy about this decision.
At this point I need to add a “Spoiler Alert.” If you have not seen the movie and want to be in suspense as to why D-Day was moved to June 6th, stop reading here and come back. If you cannot wait, read on!
On Sunday, June 4th, Krick had predicted a sunny day. While Ike’s staff was in church, a huge thunderstorm came up. The decision to postpone became more acceptable. However, later that evening, data from a civilian weather station sent information that startled Stagg. One of his staff gave Stagg a sheet of paper and pointed to a number. Stagg immediately went across the room and showed the number to Krick. Krick was just as startled. They sent for General Eisenhower and explained that the number (we never find out what that number is) meant that there would be a 24 hour “gap” in the storms. This meant the invasion could be moved one day later to June 6th. Not even the Germans would know about this gap, which is the basis of what Ike said to JFK some years later as what the key element to the success on June 6th was: “We had better meteorologists than the Germans.”
But this is not the end of the story. The next day after my wife and I watched “Pressure”, I realized what the number on the piece of paper had to be (though never stated in the movie), and why Stagg and Krick were both startled and why Ike learning what the number meant had no reservation to moving the invasion by just one day. I believe that the number was surely atmospheric “Pressure”! At the core of the equations that explain the motion of any storm is the Bernoulli Equation. Basically, it says that as pressure goes up, the velocity must go down, and vice versa. The number on the piece of paper had to be a pressure much higher than what Stagg had seen up to that point, which meant the storm was getting weaker, at least for 24 hours. “A Gap!” So the name of the movie seems to have two meanings: “emotional” Pressure associated with the monumental decisions facing Ike and others that fateful day, and “atmospheric” Pressure, a number that made it clear it was the right decision to take advantage of “the gap” in the storms. So, there was “Pressure”, and there was “Pressure.” – Dr. Tom
