Complex sentence: Like other SLBMs the initial launch was powered by a gas generator in the bottom of the firing tube, during the missile's passage through the water additional motors produce a gaseous wall around the missile, reducing hydrodynamic resistance.
Split into simpler sentences: Like other SLBMs the initial launch was powered by a gas generator in the bottom of the firing tube. During the missile's passage through the water additional motors produce a gaseous wall around the missile, reducing hydrodynamic resistance.