The launching of the satellite Sputnik, the first satellite in the world.
The plural of the noun "first" (an inaugural or premier accomplishment) is firsts.E.g. "The Soviet Union was responsible for many firsts in space exploration."
first President of the country.
Soviet Union
First man in orbit, for the Soviet Union.
the Soviet Union
I think it was the Soviet Union
The Soviet Union.
Poland
The Soviet Union (USSR)
the soviet union
Soviet Union
Leningrad is in the former Soviet Union, named after the Soviet Union's first Communist dictator, Lenin.