The U-612 used during filming is a non-diving u-boat replica of the US Navy submarine S-33 built in Valetta, Malta. It was heavily modified but is the same watercraft used for U-571 (2000).
German submariners had the lowest survival rate of any branch of service of any country during World War Two. Of the some 40,000 men who served on U-boats, 33,000 were killed.
On August 4 1942, the real U-612 was accdentally rammed off Danzig by U-444 during trials after construction. She sank with the loss of two men. After refloating and repairs she was deemed unfit for front line action and so was used as a training submarine until the end of the war. On May 2, 1945 she was scuttled to avoid imminent capture by the Russians. She never saw action.
Filming of the eight episodes of season 1 took place from 31 August 2017 through to 20 February 2018 (105 days) on location in and around Munich, La Rochelle, Prague and Valetta.