Complex sentence: They contact the Royal Navy and the People's Liberation Army Air Force to explain Carver's scheme, then find and board Carver's stealth ship in Ha Long Bay to prevent him firing the stolen British cruise missile at Beijing.
Split into simpler sentences: They contact the Royal Navy and the People's Liberation Army Air Force to explain Carver's scheme. They find Carver's stealth ship in Ha Long Bay and board it to prevent him firing the stolen British cruise missile at Beijing.