Complex sentence: Soyuz 19 was also the first Soviet spacecraft to which a foreign flight crew had access before flight; the Apollo crew were permitted to inspect it and the launch and crew training site, which was an unprecedented sharing of information with Americans about any Soviet space program.
Split into simpler sentences: Soyuz 19 was the first spacecraft to which a foreign flight crew had access before flight. The Apollo crew were permitted to inspect Soyuz 19 as well as the launch and crew training site, which was an unprecedented sharing of information with Americans about any Soviet space program.