As a student of this course, I have quickly learned that breaking codes and deciphering texts is not the easiest of tasks, and the harder the codes become, the harder it becomes to crack them (obviously).
Chapter 5 of Liza Mundy's book "Code Girls" describes the beginnings of women working as code breakers for the Allies in World War II and just how difficult it actually was. Working on a day to day basis with a group of women where only a small handful were able to work at the expectations of the military, this became increasingly frustrating as more American ships started to crumble and the Allies started to lose the war on many fronts. In fact, it become so increasingly difficult that they described it as "heart-rendering", hence the title of this chapter.
Even despite all of this, those handful of women "rose to the challenge", working collectively to break up to hundreds of thousands of codes every month. This was a major turning point, especially on the naval front. Germany's naval codes were now not as uncrackable as they once seemed, and the cryptanalyst's eye could catch Japan's mistakes within their messages. It almost seemed as though codes became easier to break as the enemies tried to complicate their codes further. This, along with a series of breakthroughs, is what I believe to be one of the key differences makers in this war.