List of the largest ships hit by U-boats in World War I

During the First World War, U-boats of the German Imperial Navy (Kaiserliche Marine) and the Austro-Hungarian Navy (Kaiserliche und Königliche Kriegsmarine or K.u.K. Kriegsmarine) sank over 6,000 Allied and neutral ships totaling over 14,200,000 tons. Many additional ships that are not included in those totals were damaged, but were able to return to service after repairs. This list contains the approximately 100 ships over 10,000 tons that were either damaged or sunk by U-boats by torpedoes, submarine-laid mines, gunfire, or other means.

List
Ships listed are presented in descending order on the tonnage figure. Those that were damaged are indicated with an asterisk after their names. Three ships—RMS Justicia, RMS Celtic (1901), and HMT Southland—appear on the list twice. Justicia was damaged by SMU UB-64 (Germany) on 19 July 1918 and sunk while under tow the following day by SMU UB-124. Celtic was damaged by SMU U-80 and SMU UB-77 in separate incidents in February 1917 and March 1918, respectively. Southland was seriously damaged by SMU UB-14 in September 1915 and sunk by SMU U-70 in June 1917. All U-boats listed are German unless otherwise noted in the table.

Kapitänleutnant (Kptlt.) Otto Weddigen in SMU U-9 sank three Royal Navy cruisers that appear on the list—HMS Aboukir (1900), HMS Hogue (1900), and HMS Cressy (1899)—in a little more than an hour during the action of 22 September 1914. The first three victims of UB-14's career—the ITALIAN ARMORED CRUISER Amalfi, the British troopship HMT Royal Edward, and the troopship HMT Southland (which was seriously damaged) in July, August, and September 1915, respectively—are all on the list.

Four U-boat commanders appear four or more times on the list. Kptlt. Hans Rose in SMU U-53 sank two ships and damaged two others between June 1917 and April 1918, while Kptlt. Otto Steinbrinck in SMU UC-65 did the same between March and July 1917. Between October 1916 and October 1918, Kptlt. Wolfgang Steinbauer sank three ships on the list in SMU UB-47 and damaged a fourth in SMU UB-48. Kptlt. Gustav Sieß—responsible for sinking the largest ship on the list, the hospital ship HMHS Britannic struck a mine and sunk (the younger sister ship of RMS Titanic and RMS Olympic)—topped the list with five entries, four (including Britannic) sunk in SMU U-73 and a fifth sunk in SMU U-33 (Germany), all between April 1916 and April 1917. Other notable commanders that appear on the list are Kptlt. Lothar von Arnauld de la Perière (three times) who sank the most tonnage of any submarine commander ever, and Linienschiffsleutnant Georg Ritter von Trapp of the Austro-Hungarian Navy (two times), known as the patriarch of the family made famous in The Sound of Music and its subsequent film adaptation.