The simple answer is both. When 617 Squadron was first formed in late March 1943 none of the special modified 'Provisioning' Lancasters had yet been converted to carry the Upkeep mine. So much of the early training was carried out on standard Lancasters. The first modified Lancaster arrived on 8 April, and a total of 13 had been delivered by the end of that month. (Source: The Dambusters Raid by John Sweetman, 2002, p.108)
