British cruisers world war I into aircraft carriers

  I suspect its unlikely as the Town class were in service and playing a role in operations in the North Sea.  Vindictive was still under construction when altered so wasn't reducing the actual existing fleet strength which either side of Jutland was still considered very important. 

  Not of currently existing and useful warships.  You could see more merchant ships modified as either seaplane or aircraft carriers and possibly more hulls under construction/designs that proved impractical as with Glorious, Courageous and Furious later in OTL. 

  I've toyed with a TL one aspect of which is that Fisher's attempt to sail Courageous and Glorious under the radar so to speak as very large light cruisers - since the government had decided not to start new capital ships as they would be unlikely to be completed before the war ended - had been discovered.  If so at the very least he gets a slap on the wrist and work on them is suspended.  This leaves two [three counting Furious] large hulls that just possibly someone might see as the basis for what we would now think of as carriers.  Probably unlikely but you could end up with something like the OTL conversions - even if flush deck form - by say late 1917 or 1918 which might make the planned attack on the HSF something that occurs before the armistice.  Which would have a lot of butterflies, especially if it was successful.