Complex sentence: The USSR expressed its gratitude to the regiment by offering 37 (40) unit's Yak-3s to France, to where the pilots returned to a heroes' welcome in Paris on June 20,1945.
Split into simpler sentences: The USSR expressed its gratitude to the regiment by offering 37 of the unit's Yak-3 fighters to France. The pilots returned to a heroes' welcome in Paris on June 20,1945.