Complex sentence: After the invasion of Russia in June 1941, the Germans captured large stockpiles of Shvetsov M-25A radial engines, rated at 700-800 takeoff horsepower, depending on model, but they proved to be just as underpowered as the French engines.
Split into simpler sentences: After the invasion of Russia in June 1941, the Germans captured large stockpiles of Shvetsov M-25A radial engines, rated at 700 to 800 takeoff horsepower, depending on model. But they proved to be just as underpowered as the French engines.