One thing I heard, and have absolutely no idea if it's correct, is that submarines are given giant hard drives to have uncrackable encryption. Basically, use a

One thing I heard, and have absolutely no idea if it's correct, is that submarines are given giant hard drives to have uncrackable encryption. Basically, use a sufficiently secure source of randomness to produce a couple copies of an enormous (terrabytes, probably) one time pad. When the sub comes to port, deliver the drive using armed guards. When sending or receiving a message, use a section of the random data to XOR your message. If each section is only used once, none of the data can be decoded by someone without the one time pad. I also imagine the NSA is willing to give an honest helping hand to the US military. Whereas any other entity has to hope any help from the NSA is honest, and likely doesn't include the best known bits.