 Complete the following phrase:  A long, unobstructed bomb bay meant that the Lancaster could take the largest bombs used by the RAF, including the , and blockbusters, loads often supplemented with smaller bombs or incendiaries. The Lanc, as it was known colloquially, became one of the most heavily used of the Second World War night bombers, delivering 608,612 long tons of bombs in 156,000 sorties. The versatility of the Lancaster was such that it was chosen to equip 617 Squadron and was modified to carry the Upkeep bouncing bomb designed by Barnes Wallis for 