probably why Kim had to make all those personal visits to China

https://www.popularmechanics.com/military/weapons/news/a28209/navy-spy-sub-jolly-roger-uss-jimmy-carter/

Sep 14, 2017

A U.S. Navy attack submarine capable of carrying out top-secret undersea missions recently returned home flying the Jolly Roger—that skull and crossbones pirate flag. But why?

Operating from Naval Base Kitsap, the Jimmy Carter's area of operations is the Pacific Ocean and beyond. The obvious mission area is a small Asian country that has recently made the headlines for its nuclear and missile tests: North Korea.

What could the Jimmy Carter be doing around North Korea? Well, for starters, many of North Korea's recent missile tests, including a failed test on March 22nd, have been at a site near Kalma International Airport, near the city of Wonsan on the country's east coast. This site is a stone's throw from the Sea of Japan.