Unfortunately there were many submarines sunk in the Atlantic and Pacific theatres during WWII. Some of them have been located and recovered, but many have not. With the data we have about the last known whereabouts based on radio transmissions from many of these subs, it’s pretty easy to find them. But not all of the ships provided enough information to make recovery easy.
Even with all the information available about the mission and potential wreckage location, it took nearly 80 years to finally locate one particular sub and find closure for the families of the 80 sailors on board.