North Korea conducted the first flight test of a new submarine-launched ballistic missile last month, defense officials said this week.

The flight test of what the Pentagon is calling the KN-11 missile took place Jan. 23 off the coast of North Korea from a sea-based platform—not a submarine—located off the coast of the communist state, said officials familiar with reports of the flight test.

U.S. intelligence ships and aircraft monitored the test and tracked the successful missile firing.

Additional details of the flight test could not be learned. A Pentagon spokesman declined to comment on the test, citing the sensitivity of information about North Korea’s SLBM program.

The flight test followed a land-based ejection test of the KN-11 in November from a static launcher located at the North’s Sinpo South Shipyard in November. Sinpo is a port city on North Korea’s southeastern coast about 100 miles from the Demilitarized Zone separating North Korea from rival South Korea.

The flight test is being viewed by U.S. intelligence analysts as a significant step forward for Pyongyang’s submarine-launched ballistic missile program. The new program was first disclosed by the Washington Free Beacon Aug. 26.

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