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There is a reference to the co-operation on Astronomical Ephemerides during World War 2 in each of the two papers below, though both those references are much less detailed than the abstract in English of the Heidelberg book that Wolfgang Köberer and David Pike have highlighted.

Regards

Adrian F

Paper in Popular Astronomy, "German Astronomy during the War" by Gerard P. Kuiper (1946), page 263

https://articles.adsabs.harvard.edu//full/1946PA.....54..263K/0000263.000.html

Paper from the U.S. Nautical Almanac Office Sesquicentennial Symposium, "The History of the British Nautical Almanac Office" by George A. Wilkins (1999), page 60

https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1999naos.symp...55W&db_key=AST&page_ind=5&data_type=GIF&type=SCREEN_VIEW&classic=YES