The German Navy U-Boat pens at Bergen, Norway were attacked by a force of 32 Lancaster and one Mosquito aircraft, drawn from Nos. 9 and 617 Squadrons RAF, both units being experienced in the use of "Tallboy" bombs. Contemporary reports recorded that three "Tallboy" bombs caused serious damage to the U-Boat pens after penetrating their 3.5-meter concrete roof. Two submarines suffered minor damage, a cargo ship was severely damaged and a minesweeper was sunk. Four Lancaster bombers were lost (one from No. 9 Squadron and the others from No. 617 Squadron).