North Korea Unveils the Completed Hull of What It Calls a Nuclear Submarine

 

Why a nuclear submarine is better than diesel-electric one?

 

A nuclear submarine is superior to a diesel-electric one primarily due to its unlimited submerged endurance, greater speed, and unmatched range, thanks to its air-independent reactor, allowing it to stay hidden and operate globally for months without refueling. While diesels are quieter and better for coastal defense, nuclear subs excel at power projection, high-speed sprints, and long-duration patrols, limited only by food, not fuel or air, making them far more strategically flexible and capable.

 

Key Advantages of Nuclear Submarines

 

    Unlimited Endurance & Range: Nuclear reactors don't need air, so they can stay submerged for months, even years, limited only by food and crew supplies, giving them global reach.

    High Speed & Power: The immense power allows nuclear subs to maintain high speeds (25+ knots) for extended periods, crucial for keeping pace with carrier groups or escaping threats.

    Stealth (Strategic): While diesels are quieter at low speeds, nuclear subs can remain hidden indefinitely at great depths, making them nearly impossible to track for long patrols.

    Power Projection: Their range and speed make them ideal for offensive missions, monitoring enemies across oceans, and deploying anywhere globally.

    Advanced Systems: More power supports sophisticated sonar, communication, and life support, enhancing mission effectiveness and crew comfort.

 

Where Diesel-Electric Subs Compete

 

    Coastal Defense: Their smaller size and quiet battery power make them ideal for ambushing in shallow, coastal waters.

    Cost & Simplicity: They are cheaper to build, operate, and crew, making them accessible to more navies.

 

The Trade-Off: A "Two-Choice" Problem

 

    Diesel-electric subs with Air-Independent Propulsion (AIP) can stay submerged longer than traditional diesels but still can't match nuclear subs' speed/range combo.

    Nuclear subs do everything well: long range, high speed, and deep, sustained submerged operations, making them the choice for blue-water power projection.

 

In essence, nuclear submarines are strategic assets for global power projection, while diesel-electric submarines are tactical assets for regional coastal defense, with nuclear providing unmatched strategic flexibility.

 

 

 

“The debut followed the North’s first test of a new surface-to-air missile and the arrival of a U.S. nuclear-powered attack sub for a port call in South Korea.

 

The arms race between North and South Korea has expanded underwater as the North ​on Thursday condemned the South’s plan to build a nuclear-powered submarine as a security threat and unveiled​ the completed hull of its ​own nuclear sub, which is under construction.

 

North Korea’s leader, Kim Jong-un, ​had designated building a nuclear sub as one of his top weapons projects during a Workers’ Party congress held in 2021. In March, North Korea’s state media​ carried photos showing such a vessel under construction. ​On Thursday, the state media ​carried photos of Mr. Kim inspecting the completed hull of what it called a nuclear-powered strategic guided missile submarine.

 

​Outside officials and analysts have long questioned how soon North Korea would be able to acquire complex technologies and components ​for a nuclear submarine, and how and from where it would supply the small nuclear reactor​ needed to power it.​ The unveiling on Thursday indicated that North Korea ​was making progress, although it has yet to announce when it expects to finish and deploy the vessel.

 

​The completed and welded hull “means that they have already mounted a nuclear reactor inside,” said Hong Min, an expert on the North Korean military at the Korea Institute for National Unification, a government-funded think tank based in Seoul.

 

Mr. Hong suspected that North Korea was ​receiving technological help from Russia in return for having sent troops and weapons to aid Moscow’s efforts against Zelensky.

 

The North Korean sub appeared to be designed to carry ballistic and cruise missiles, as well as torpedoes​, military experts said. North Korea has been testing various submarine-launched missiles and torpedoes in recent years, claiming that they were built to deliver nuclear warheads.

 

It said its nuclear weapons development was justified by a growing military threat it felt from the United States and its Asian allies, Japan and South Korea.

 

​On Thursday, Pyongyang bristled at the arrival of the U.S.S. Greeneville, a Los Angeles-class American nuclear-powered attack submarine, at a naval base in Busan at the southeastern tip of South Korea this week. South Korea’s Navy said the American vessel made the port call to replenish supplies and to allow its crew members to rest. North Korea’s Defense Ministry called it “a grave act of causing instability and escalating military tensions.”

 

Also on Thursday, North Korea said Mr. Kim inspected the first test of a new high-altitude, long-range surface-to-air missile under development. During the test, which was conducted on Wednesday, the missiles hit mock targets at an altitude of 124 miles, it said.

 

The South Korean military confirmed the launching of several land-to-air missiles by the North, but did not provide details.

 

In November, the United States agreed to help South Korea build its first nuclear-powered submarine to strengthen its navy’s ability to patrol waters around the Korean Peninsula. South Korea said its nuclear-powered submarines would not carry nuclear weapons. It said it felt no need to build nuclear weapons because the United States provided it with nuclear-umbrella protection.

 

​But Mr. Kim said North Korea regarded the South Korean project as “an offensive act” and “a threat to its security that must be countered.” It compels North Korea to accelerate “the modernization and nuclear weaponization of the naval force,” he said.

 

Such efforts by Mr. Kim have gained momentum since events in Ukraine. Mr. Kim has aided Russia’s efforts by sending troops and large shipments of artillery shells, missiles and other weapons. South Korean intelligence officials and analysts said Russia had reciprocated by providing North Korea with fuel and food, plus materials and technologies to help modernize its military, including its decrepit navy and air-defense systems.

 

North Korea is expected to hold its party congress early next year. The congress, held once every five years, is the most important political event in North Korea​, where Mr. Kim ​will likely show his military achievements and set new policy goals for the next five years.” [1]

 

1. North Korea Unveils the Completed Hull of What It Calls a Nuclear Submarine. Choe Sang-Hun.  New York Times (Online) New York Times Company. Dec 25, 2025.