Though Operation Chastise, the dams raid, succeeded in breaching two dams, it was at the cost of 8 of the 19 aircraft involved. The next major operation undertaken by 617 Squadron was a low-level attack on the Dortmund-Ems canal and suffered even heavier proportional casualties, five of eight aircraft were lost (plus one the previous day on an aborted raid) and the canal suffered no damage. Such low-level attacks were clearly unsustainable, especially without the element of surprise - the defences of German damns were immediately reinforced after the raids, for the rest of the war 32 flak batteries and four and a half balloon batteries were devoted to protecting dams. 617 instead switched to precision bombing from high altitude using the Stabilised Automatic Bomb Sight (SABS) and enormous Tallboy and Grand Slam bombs on targets including the battleship Tirpitz and, a year after the catastrophic low-level attack, the Dortmund-Ems canal.