On the night of April 22 to 23, 1918, the Royal Navy carried out a daring operation to block a key canal in Belgium used by German submarines. The plan involved deliberately sinking three old cruisers—Thetis, Intrepid, and Iphigenia—filled with concrete at the entrance of the Zeebrugge canal. The goal was to prevent German U-boats from using this route to bypass British minefields in the English Channel and North Sea. However, the operation resulted in significant loss of life, with 176 deaths, 412 injured, and 49 missing. Only one of the three ships sank at the intended location, leaving a gap that the Germans quickly repaired by dredging and widening the canal. The idea for the operation came from Rear Admiral Roger Keyes, who was responding to the growing threat of German submarine warfare. At the time, U-boats were frequently using Belgian canals to avoid British naval defenses, with as many as thirty incursions per month. The plan was to use obsolete warships filled with concrete to create a permanent blockage. However, the execution was flawed. Two of the three ships ran aground slightly off course, and the third, Thetis, sank in the right place but left an incomplete barrier. This allowed German engineers to quickly fix the canal, restoring the passage for U-boats. The British fleet approached the Belgian coast under the cover of darkness, but the flagship, HMS Vindictive, docked in a position that made the operation more difficult. A British submarine, HMS C3, also faced challenges, becoming stuck between metal pillars of a bridge before detonating explosives. Despite these setbacks, the operation was marked by bravery and sacrifice. However, the technical failure of the blockage allowed the Germans to continue their submarine attacks. Although the Zeebrugge operation failed to achieve its military objective, it was widely publicized in British propaganda as a heroic effort. Several sailors were awarded the Victoria Cross for their actions during the mission. The event remains a poignant example of the risks and challenges faced by naval forces during World War I.