multiple sorties at night?

[Nick Powell]

Hi All
It was suggested that I post this question here.
I am a regular on the RAF commands forum and there is a similar thread running there that is generating some discussion!
My son came home from school after a history lesson having been told that German bomber crews would make more than one trip to London in a single night, can anyone advise if this is correct or not.
It stems from a discussion about the length of time that a raid would take.There seems to be an assumption that because civilians sometimes spent 12 hours in a shelter that that was how long a raid took!I explained that it would have been different groups coming in one after the other essentially several raids in one night so it made sense to stay put in the shelter.
His teachers explanation was that a crew would return to base re arm and fly straight back to London thus allowing a raid to go on all night! A rolling raid.
What was the case?

TIA nick