Complex sentence: A combination of rain and snowstorms scattered the airships while they were still over the North Sea: none of the naval airships reached London, only the army's LZ 98 and the newly commissioned Schütte-Lanz SL 11 reaching their objective.
Split into simpler sentences: A combination of rain and snowstorms scattered the airships while they were still over the North Sea. Only the army's LZ 98 and the newly commissioned Schütte-Lanz SL 11 acheived their objective.