I think all three of RBMK, Skipped Once and Goldbricker are correct.
In essence - Hermes/Viraat is the oldest-surviving British aircraft carrier. The British gets deleted in many references, which starts the possible confusion. This is compounded by the discussion of whether the 'oldest carrier' means still extant, even if the ship last sailed decades ago; theoretically capable of use as a carrier if refurbished/refitted or actually in service as a carrier.
The reason for this is that some authorities appear to consider museum ships to be a role conversion - so although Intrepid (say) was an aircraft carrier and looks like an aircraft carrier, it isn't. There are further definitions - for example, could tugs move the ship from its current location, with a crew steering the ship? If not, it's definitely a floating museum and no longer a carrier (or a frigate, or whatever the ship entered service as). Other authorities consider this overly-fussy/pedantic and consider Yorktown (say) to be an aircraft carrier, even if the ship is now a museum. I have to say that I tend to sympathise with this latter definition, otherwise you end up having to decide whether to describe HMS Victory as a museum, a 104-gun first rate ship of the line or a command ship (as Victory is the flagship for 1SL).
For our purposes though, under one definition, RBMK is correct, under another Skipped Once and Goldbricker are right.
We hope you enjoyed tonight's pedants' corner and return you to your scheduled discussion with a reminder that when Hermes was transferred to the Indian Navy, the newly-named Viraat was commissioned/launched by the Indians by the ceremonial breaking of a Bounty Bar across the forward hawser...
