The reason that HMS Illustrious was there and the rest of Greenwich was buzzing was to celebrate the centenary of the Royal Navy Air Service. Now I wasn't going to argue when I was told this, but I did wonder. So, I started investigating when I got home. The official website
cites 1912 as the start date, but poke around and the ever-reliable Wikipedia comes up with the goods: ...the use of aircraft for military and naval purposes should be investigated....a rigid airship based on the German Zeppelin be designed and constructed by the firm of Vickers. After much discussion on the Committee of Imperial Defence the suggestion was approved on 7 May 1909. The airship, named Mayfly, never flew and broke in half on 24 September 1911."
You couldn't make it up.