At a guess I'd say that a number of them are regarded as Top Secret, a big issue would be hard to cover up. Although I'd imagine if there were many issues they

At a guess I'd say that a number of them are regarded as Top Secret, a big issue would be hard to cover up. Although I'd imagine if there were many issues they be known about. I'd love to learn morea about nuclear reactors on carriers and submarines, but I imagine most of the engineering knowledge is secret.