On what date did the USS Thresher experience a flooding casualty?

The USS Thresher experienced a flooding casualty on April 10, 1963, which is a crucial historical event in naval history. This tragic incident involved the submarine sinking during deep-diving tests off the coast of Massachusetts, resulting in the loss of all 129 crew members on board. The submarine's sinking prompted significant changes in submarine safety measures and protocols, leading to increased scrutiny and improvements in submarine design and operation. The date is significant as it marks a turning point in naval operations and safety standards that were implemented in the following years to prevent similar disasters.