Okay, so you know how sometimes big machines called submarines can go underwater like fish? Well, sometimes during war, one country might use a submarine to attack another country's ships. This can be really dangerous and can cause a lot of people to die.
Now, there have been a bunch of times throughout history where submarines have sunk big ships. This means that the ships go underwater and can't come back up, and the people on the ship might get hurt or even drown.
So, people have made a list of all the times this has happened and how many people died each time. At the top of the list is the USS Indianapolis, a big ship that was sunk by a Japanese submarine in World War II. Over 800 people died in that one.
Other ships on the list include the RMS Lusitania, which was sunk by a German submarine during World War I and over 1,100 people died, and the HMS Barham, which was sunk by a German submarine during World War II and over 800 people died.
It's really sad that so many people have died because of submarines sinking ships, but thankfully we're better at protecting ships now and there haven't been as many incidents like this in recent times.