Regular training in the escape drill trainer.
'Emergency Procedures Briefings' were not given in the same long-winded manner you hear these days. he crew knew what to do. If the aircraft had to be abandoned, the captain would just order 'OUT, OUT!' or words to that effect and the rear crew would react instinctively. If the undercarriage was down and couldn't be raised in sufficient time, the navigators and AEO were supposed to grab the door jacks and twist round them to try to avoid the noseleg.
There was a film of a fit parachute training instructor doing it in a wind tunnel - he was only just able to avoid the noseleg. The average chubby aircrew person wouldn't have stood a chance.
We did all our visual circuit pattern work with the undercarriage down - it gave the rear crew an opportunity to whinge more than normal about pilot play time.