Complex sentence: The US Navy also experimented with a version of the Tiny Tim which was a two-stage rocket, with another Tiny Tim rocket motor mounted behind a complete Tiny Tim. Like the Richard it never moved beyond the R&D stage.
Split into simpler sentences: The US Navy also experimented with a version of the Tiny Tim which was two staged. With another Tiny Tim rocket motor mounted behind a complete Tiny Tim. Like the Richard it never moved beyond the R&D stage.