U.S Military has recently uncovered evidence that North Korea has been engaging in “highly unusual and unprecedented levels” of submarine activities in the country since North Korea’s second intercontinental ballistic missile launch this month.

It was revealed Monday, by an unnamed U.S. defense official that North Korea carried out an “ejection test” Sunday at the Sinpo Naval Shipyard on the country’s eastern seaboard.

According to U.S. intelligence assessments, Pyongyang’s (North Korea) submarine fleet comprises about 70 subs, but few are thought to be new or sophisticated enough to fire missiles and the submarine-based launch program is still in its nascent stages.