Two separate recording sessions took place on this day at Abbey Road's Studio Three.
The first was for overdubs onto Revolution, which was destined to be part of The Beatles' next single. Session player Nicky Hopkins added electric piano to track four on the tape, playing a solo and again in the coda.
The electric piano overdub took up the whole of the 4-7pm session. The second session that evening began with three saxophones added to Ob-La-Di, Ob-La-Da. The session performers' names were undocumented.
The Beatles then turned their attention back to Revolution. A third reduction mix - take 16 - was made, which combined tracks three and four onto the third track of a new tape. Paul McCartney then recorded a bass guitar part, but it was re-recorded the next day.
Risking the antagonism of the studio engineers and tape operator, The Beatles then returned to Ob-La-Di, Ob-La-Da. Another reduction mix was created, which was numbered take 23. McCartney then double-tracked his bass guitar line, as the original had become buried in all the previous mixes.
The session ended at 3.45am, after two mono mixes of Ob-La-Di had been created. These were improved upon on 12 July 1968, but McCartney re-recorded his lead vocals on 15 July, rendering them unnecessary.