The Who's 1972 top 20 hit, "Join Together", was supposed to be on a studio album, but the planned record was never released, and "Join Together" and two other singles were released anyway.
For what it's worth, all four members of the band actually played versions of the harmonica on the track. The only one who doesn't in the video that I can see is drummer Keith Moon.
The harmonica Pete Townshend uses has to be one of the biggest known to man. Period.