As a security measure the U.S. Navy limits the number of electronic devices the crews of SSBNs (ballistic missile carrying nuclear subs) can bring on board. That means no electronic book reading devices (like iPads or Kindles). That’s annoying to the crew, who like to read in what little spare time they have. Space is limited on a sub and you can’t bring that many books (even paperbacks) on board. So the navy came up with a solution, a book reader with no networking capability and no data connectors (like USB). Called the NeRD (Navy eReader Device) it is pre-loaded with 300 books and only has a port to have its battery recharged. Five are being sent to each nuclear sub so the crews can try them out.
Books can be added or deleted but you have to disassemble the device and replace the NAND Flash data chips. This does not make it impossible for a spy on a nuclear sub to use a NeRD device to store data stolen from submarine systems, but it would be impractical. For the effort required there are easier ways to take data. That appears to be the thinking behind the way NeRD was designed. If the user tests are a success a device like NeRD has space for thousands of books. The navy runs surveys to find out reading preferences of its submariners and thus periodically update the selection available on the NeRDs.