Zeppelin's ideas for large airships were first expressed in a diary entry dated 25 March 1874. Inspired by a recent lecture given by Heinrich von Stephan on the subject of "World Postal Services and Air Travel", he outlined the basic principle of his later craft: a large rigidly-framed outer envelope containing a number of separate gasbags. In 1887 the success of Charles Renard and Arthur Krebs' airship "La France" prompted him to send a letter to the King of Württemberg about the military necessity for dirigibles and the lack of German development in this field.