The OCU is for new pilots transitioning onto the aircraft.
Jesus, I thought it was for people to bum around
No seriously though, 'squadron A' returning to the UK in December '18 and an OCU standing up in Marham in '19 reads to me like 'squadron A' and the OCU are going to be the same thing. Yes there will be a cadre of pilots capable of landing on an aircraft carrier, but if the OCU is only being stood up in 2019, then I get a distinct impression there won't be nearly enough aircraft on the frontline by 2020 to 'do' fixed wing carrier ops.
I appreciate the pilots and the planes will both be capable of landing on a boat, but as biggus has alluded to, that is very different to being able to sustain a fixed wing carrier deployment!