The Ministry of Defence is looking for ideas on how best to preserve the legacy of the Royal Navy's Invincible-Class aircraft carriers.The last of the ships, 'HMS Illustrious', is due to retire in late 2014 after 32 years of distinguished service that has seen her involved in operations around the world. Following the announcement last year that the 22,000-tonne ship will be preserved in some form, MOD is now inviting private companies, charities and trusts who are interested in buying her to come forward with ideas for her future use.