This photograph of U-889 shows the small target presented by a submarine operating at periscope depth.

The attack periscope (left) tracked targets and provided data for torpedo attacks, while the larger search periscope (centre), with a wider field of view, could more easily search the sea and sky for potential enemies. The Schnorkel (right), which allowed U-Boats to operate just below the surface while being driven by their Diesel engines, was a response to the threat of Allied aircraft which, by mid-1943, had made it virtually impossible for U-Boats to survive on the surface.

George Metcalf Archival Collection
CWM 20010066-042_4