Ernst Haenchen (1894-1975), The Acts of the Apostles: A Commentary
, tr. Bernard Noble et al. (Philadelphia, The Westminster Press, 1971), p. vii:
Probably neither of these things would have come about had I not had to travel to Switzerland for a cure in 1944. It was then strictly forbidden to take books across the frontier. Only in Davos did I discover that Nestle (thin-paper edition) had made the journey with me in my coat pocket. This was all I had when I began to occupy the time of my convalescence with some serious work. That was a great blessing. For when I now sought to penetrate more deeply into Acts, I was not led astray by any secondary literature which was primarily interested in Luke's sources. So I came quite independently to the question what the author of Acts had wanted to say to his readers through the varied scenes of his book, and I sought myself to become his reader.