Complex sentence: The "Wespe" first saw combat in 1943 on the Eastern Front, and proved so successful that Hitler ordered all Panzer II chassis production to be reserved for the "Wespe" alone, dropping other projects such as the Marder II self-propelled anti-tank gun.
Split into simpler sentences: The "Wespe" first saw combat in 1943 on the Eastern Front. It proved very successful, and Hitler ordered all production of Panzer II chassis to be utilized in the production of the "Wespe" alone, dropping other projects such as the Marder II self-propelled anti-tank gun.