Complex sentence: The initial RD-45 proved troublesome due to Soviet inexperience with engineering and materials, but was further improved to produce the VK-1 which differed from the Nene in having larger combustion chambers, larger turbine, and revised airflow through the engine.
Split into simpler sentences: The initial RD-45 proved troublesome due to Soviet inexperience with engineering and materials. The RD-45 was further improved to produce the VK-1 which differed from the Nene in having larger combustion chambers, larger turbine, and revised airflow through the engine.