Specifically, the Los Angeles class boat the USS Toledo:

Two cracks have been discovered on the hull of the USS Toledo, a potentially fatal flaw that could have led to water leaks and, ultimately, hull failure if the submarine submerged, the Navy confirmed Tuesday.

Toledo crew members on Friday found the 21-inch-long crack in the exterior topside hull under the sail and a corresponding 1-inch crack in the pressure hull underneath.

From the picture, it’s one of the later models of the Los Angeles class, it has bow planes, not sail planes, so it should be well before the fatigue life of the hull is reached, and it was found by the crew, but still, cracks in pressure hull of a sub…Yikes!!!

Hopefully this is a one-off, and not a systemic problem.