The battle of Midway was a historic turning point for the US during World War II. Joe Rochefort was the officer in charge of Station Hypo, a group of hand-picked Navy cryptographers tasked with breaking the Japanese Navy cipher. The machine the Japanese used was the JN-25. Unlike the British Bletchley Park cryptographers trying to break the Enigma traffic, he cryptographers did not have a version of the JN-25 machine. The fascinating story of Rochefort is explained brilliantly in the 2011 book “Joe Rochefort’s War” by Elliot Carlson.
Recently, Chris Christensen of Northern Kentucky University, one of the top historical experts on the US Navy cryptographers during WWII, have two lectures on the mathematics behind breaking the JN-25 ciphers.

45 minutes:

30 minutes: