Hansard HC Deb 26 March 1969 vol 780 c303WCruisers (V/STOL Aircraft) "Mr. Wall asked the Secretary of State for Defence whether the new cruisers will operate vertical/short take-off and landing aircraft; and when it is expected the first will be ordered. Mr. John Morris No decision has yet been taken whether vertical and short take-off and landing aircraft should be operated at sea. It is too early to say when the first of the new cruisers will be ordered."
Hansard HC Deb 04 March 1977 vol 927 c337W, this lists Invincible as ordered in financial year 1973–74, the explanation for this is given in the following source: Hansard HC Deb 24 November 1977 vol 939 cc869-70W Question to the Secretary of State for Defence about contracts, 24 November 1977. For the first ASW Cruiser (HMS Invincible) the planned order date when tender invited was February 1973. The contract was placed in April 1973.
Wright, Anthony (June 1998) [1978]. Australian Carrier Decisions: the acquisition of HMA Ships Albatross, Sydney and Melbourne. Papers in Australian Maritime Affairs (No. 4). Canberra: Sea Power Centre. p. 167. ISBN0-642-29503-4. ISSN1327-5658. OCLC39641731.
Stevens, David; Sears, Jason; Goldrick, James; Cooper, Alastair; Jones, Peter; Spurling, Kathryn (2001). Stevens, David (ed.). The Royal Australian Navy. The Australian Centenary History of Defence (vol III). South Melbourne, VIC: Oxford University Press. p. 227. ISBN0-19-554116-2. OCLC50418095.
Hobbs, Commander David (October 2007). "HMAS Melbourne (II) – 25 Years On". The Navy. 69 (4): 9. ISSN1322-6231.