Complex sentence: Gribkov's plan included a main missile force of five regiments: three armed with R-12 medium range missiles and two armed with R-14 intermediate range missiles, each regiment equipped with eight launchers and 1.5 missiles per launcher.
Split into simpler sentences: Gribkov's plan included a main missile force of five regiments. Three would be armed with R-12 medium-range missiles and two armed with R-14 intermediate-range missiles; each regiment would also be equipped with eight launchers and 1.5 missiles per launcher.