The first attack was conducted by 43 Halifax and Avro Lancaster bombers, the second by 34 Halifax and Lancaster.[61] A combination of heavy German anti-aircraft fire and poor weather caused all three missions to fail.[60] Over the rest of the year and into late 1942, Tirpitz underwent a refit in the Faettenfjord, which lacked dockyard facilities of any type. As a result, the work was done incrementally; a large caisson was built to allow the rudders to be replaced.[63] Naval historians William Garzke and Robert Dulin stated that "the repairs to this ship were one of the most difficult naval engineering feats of World War II."[64]