Complex sentence: The first flying unit (S-23) was initially tested on the Volga River in the autumn of 1972, and the next year dismantled and transported to the Caspian Sea for continued testing.
Split into simpler sentences: The first flying unit (S-23) was tested on the river Volga in the autumn 1972. After that the craft was dismantled and transported to the Caspian Sea in 1973 for continued testing.