Crew members last Friday discovered a 21-inch crack in the topside hull, as well as a corresponding one-inch crack in the pressure hull that would have leaked water if the ship was submerged, the spokesman said.More information is in this article, which said the crack was found aft of the sail. It's a good thing the crew was conscientious about noticing this; it would have been scary to find it underway.
“The submarine was pierside in New London,” said Lt. Patrick Evans, spokesman for Submarine Group 2. “The Navy is conducting additional tests to determine the extent of the crack and the proper procedures to repair it.”
The width and location of the crack were not yet available.
“After a cause is determined, other submarines will conduct similar inspections,” he said.
Because of the one-inch crack in the pressure hull, “water would have entered Toledo if submerged,” Evans said.
Update 0946 25 July: Here's a follow-up from Navy Times, pointing out that the crew almost certainly would have found the leak soon after submerging, so the crew was never really in danger.