There's not too much to be found regarding the experiences of crews whose target was the Gironde estuary, but I have come across the following in the book "Lancaster: The Second World War's Greatest Bomber" by Leo McKinstry. Norman Ashton, a flight engineer with 103 Squadron recalled the following after his Lancaster dropped from 16,000 feet to a little under 2,000 to drop sea mines and the German defences opened up:
"The whole aircraft seemed to be wrapped in the flashes, like an ungainly Guy Fawkes perched awkwardly on a flickering bonfire. It was fantastic. I could hear, feel and smell the filthy stuff belting against the aircraft but nothing untoward happened."
As soon as the sea mines had been released, he opened the Lancaster's engines to gain altitude and head home. McKinstry's recollections clearly show the danger a Lancaster faced when gardening the Gironde.