[pdf] the Berlin Tunnel Operation (1952 – 1956)

I found this compelling to read - there was an aspect of "it's so cool they did this", but also an feeling that the people on either side of the cold war, the day to day engineers and soldiers, military and intelligence, were just people, with humor and humanity, no matter what side they happened to be on.

"The lack of an adequate base line made the surveying problem especially difficult [...] so a baseball game was organized with the objective of knocking a baseball as far into the East Zone as possible. This scheme was frustrated by the friendliness of the East German guards who kept returning the baseball."