A study of satellite imagery of North Korea’s Sinpo South Shipyard offers further signs that the country is developing a submarine capable of launching nuclear-grade missile attacks, according to 38 North, a Johns Hopkins School of Advanced International Studies website devoted to North Korea analysis.

The news comes after earlier reports from “The Washington Free Beacon,” which first reported Pyongyang’s submarine-missile ambitions in late August, citing U.S. intelligence sources.

The images posted in 38 North may also offer the clearest signs publicly available that a submarine missile may be in the works in the rogue nation.

The development, if true, would be disturbing news for the U.S., which has signed mutual defense pacts with North Korea’s two favorite targets--South Korea and Japan.

Here’s what the satellite images indicate about the installation:

DigitalGlobe

The structure is the “right size and design to be used for the research, development, and testing of the process of ejecting a missile out of a launch tube as well as evaluating its compatibility with submarines and surface combatants,” wrote Joseph Bermudez, an analyst at AllSource Analysis in the blog.

DigitalGlobe

Given the know-how and the cost required to develop submarine-launched ballistic missiles, Bermudez believes it will be years before North Korea will have an operable system. And even then, the biggest hurdle to successfully deploying submarine-launched ballistic missiles [SLBMs] could be trust.

“Aside from the technological challenge, it also assumes that Pyongyang would entrust an operational nuclear-armed missile to the captain of a submarine who would, in time of war, most likely be out of communication with the leadership,” he said.