Armored glass
Until the 1970s, the only measure to prevent attacks on or sabotage of the telecommunications network was simply to lock the front doors after closing time. After the train hijackings and hostage-taking, but also with the emergence of terrorist groups such as the Bader Meinhof and RaRa, there was a growing awareness that communication traffic was vulnerable. When a central building like this was destroyed, a recovery time of several months to a year had to be taken into account. As an extra safety measure, the access doors were reinforced and windows were fitted with triple tempered glass in some places. For example, the openings to the basement windows were welded shut and the two lower floors were fitted with armored glass. The photo shows the tempered glass that was removed from the window frame during the renovation in 2019. These pieces are two triple armored glass plates of 5 cm thick.