The first two thirds of the program limns in the history of the Pacific War beginning with the Japanese attack on Pearl Harbor and, in the end, focuses on the climactic battle for Okinawa. It could hardly have been more horrifying for the Japanese or for the American Marines, soldiers, and the US Navy, all of whom experienced immense and ultimately pointless suffering. Anyone who wants a personal view from a Marine sergeant might read William Manchester's "Goodbye, Darkness." Or try Eugene Sledge's "With the Old Breed." Both men became writers after the war and then professors.
The "secret" in this story -- and every one I've seen so far has some sort of secret -- is that the US Navy and the Brits at Bletchley Park had broken first the Japanese diplomatic code and then the Japanese naval code. It may have been tedious for the code breakers themselves but it certainly shortened the war and possibly saved it. The breaking of the Japanese codes was essential to the American success in the naval battle of Midway, which put the Japanese navy permanently on the defensive. And it enabled American P-38s to assassinate Admiral Yamamoto while he was en route to an inspection tour. The codes didn't help at the sometimes chaotic battle of Leyte Gulf, which is skipped here entirely.
What a godawful thing war is. Watching this series, one can't help wondering sometimes why some humans are so anxious to be involved in another one.