Kim Jong-un has spent much of his time as North Korea’s leader developing bigger and more advanced nuclear weapons. This year, he may try to make them harder to find by putting them under the sea.Recent North Korean reports touting a new submarine and its test of a ballistic missile designed to be launched from one have fuelled speculation that a sub may be the “new strategic weapon” Kim promised to unveil this year. While such a vessel would probably be noisy and unable to stray far from the…