Complex sentence: At Lavrenty Beria's insistence, the "RDS-1" bomb was designed similarly to the "Fat Man" bomb dropped on Nagasaki, Japan; it was an implosion type weapon with a solid plutonium core.
Split into simpler sentences: At Lavrenty Beria's insistence, the "RDS-1" bomb was designed after the "Fat Man" bomb dropped on Nagasaki, Japan. Like "Fat Man," it was an implosion type weapon with a solid plutonium core.