Complex sentence: The site was designed in January and February 1943 by engineers from the Peenemünde research facility and the Organisation Todt, and construction plans were presented to Hitler on 25 March 1943, who immediately gave the go-ahead for the project to begin.
Split into simpler sentences: The site was designed in January and February 1943 by engineers from the Peenemünde research facility and the Organisation Todt. On 25 March 1943 the construction plans were presented to Hitler, who immediately gave the go-ahead for the project to begin.