The 100th anniversary is dated back to when the first funding request for a naval airship was granted in 1909. 

A longer post on the Fleet Air Arm during CRUSADER can be found at this link. More specific to HMS Illustrious, during CRUSADER, the squadrons disembarked from HMS Illustrious served as fighters, airborne escort, target illuminators, and night bombers. Illustrious herself was out of service because of damage received in successive attacks from January to May 1941.

Click here for the Flight Global article on the centenary with some nice illustrations.

Click here for the Fleet Air Arm Archive page on HMS Illustrious in WW2.

Click here for the Fleet Air Arm Archive page on No. 815 Squadron FAA.

And some pictures, courtesy of my wife Livia.

HMS Illustrious (R06) at her moorings on the Thames at Greenwich, just north-west of the old Naval College, now the University of Greenwich

The Flypast from our 6th floor balcony close to the river

The Flypast turning over a construction site

Giving a good idea of the size of this relatively small carrier

The 1940s HMS Illustrious (R87) sailing in the Indian Ocean in 1944. Courtesy of Wikimedia Commons.

HMS Illustrious under Axis bomber attack in the Mediterranean, probably early 1941. Courtesy of Wikipedia