Here's What You Need To Remember: The most important naval battle of the war occurred on the opening day of the conflict. South Korea’s only large patrol boat intercepted and destroyed a North Korean vessel on the verge of landing troops in Pusan in an engagement described in a companion article.

Just days after North Korea embarked on its steam-roller invasion of its larger but less heavily armed southern neighbor, the United Nations decided it needed to step in and save the besieged Republic of Korea.

However, it would take time for ground forces and their heavy tanks and artillery to arrive in the South Korean port of Pusan (all the other major ports were swiftly overrun). 

The same was not true of aircraft ships based in U.S.-occupied Japan. While American jet fighters secured air superiority over North Korea’s World War II-vintage air force, it fell to the U.S. and British navies to try to stem the seemingly unstoppable North Korean advance.

The UN ships could affect battles on land in two key ways: by bombarding coastal facilities and enemy troops advancing along the coastline with their large guns, and by seizing control of the sea from North Korea’s People's Navy, which was using its small boats and merchant ships to supply troops along the coast and infiltrate commandos behind South Korean lines. 

The most important naval battle of the war occurred on the opening day of the conflict. South Korea’s only large patrol boat intercepted and destroyed a North Korean vessel on the verge of landing troops in Pusan in an engagement described in a companion article.

On July 2, a more formidable task force assembled on Korea’s eastern coastline, composed of the American light cruiser Juneau, the British cruiser Jamaica and the frigate-sized armed sloop Black Swan.

Both British vessels had seen significant action during World War II. 

The smaller escort 2,000-ton HMS Black Swan had survived mines and attacking Luftwaffe bombers and even helped sink German submarine U-124. A year earlier, she had emerged badly battered but still afloat from a deadly gun duel with Chinese coastal guns on the Yangtze River.

Jamaica’s feats were even more legendary. In 1942, she had charged towards German battlecruisers in the Battle of the Barents Sea, helping drive them away, then helped sink notorious battlecruiser Scharnhorst in the epic Battle of the North Cape.

By contrast, the 6,800-ton USS Juneau had only just been commissioned in 1946, the lead ship in her class anti-aircraft cruisers.

At a quarter past six in the morning of July 2, 1950, lookouts on the three ships spotted four North Korean motor torpedo boats (numbered No.21 through No. 24) and two gunboats (Mo-233 and Mo-234) escorting ten trawlers heading back to their bases in North Korea—having just emptied holds full of ammunition at Chuonmin Chan (also transliterated as Chumunjin).

As the cruisers surged forward to intercept, to their surprise, the motorboats peeled off and came barreling towards them!

The newly founded North Korean Navy had received at least five Soviet G-5 motor torpedo boats. The G-5s only 62 feet long, weighed a mere 18 tons and typically required a crew of six or seven. Their two 850 horsepower GAM-34 V12 engines—derived from an aircraft engine used on heavy bombers and ‘flying aircraft carriers’—could propel the boat to a blazingly fast 61 miles per hour. 

That speed was hoped to give the boats the agility to evade enemy fire and maneuver to a good firing position to release their primary weapons: two 533-millimeter torpedo tubes. While torpedoes could be dodged, they were still greatly feared: combat experience had shown that just one or two lucky torpedo hits could sink even large cruisers and carriers.

As secondary weapons, the motorboats also had 12.7-millimeter machine guns, and some may have been fitted with punchier rapid-firing automatic cannons.

The Soviet Union had built over 300 G-5s between 1934 and 1941 and lost in World War II skirmishes with the German, Finnish and Romanian forces in the Baltic and Black Seas. However, they rarely launched torpedo attacks against large warships, instead battling small minesweepers and minelayers, and serving in auxiliary transport roles. 

The two gunboats were 47-ton wooden-hulled OD-200-class submarine hunters armed with rapid-firing 37-millimeter anti-aircraft cannons, sonars, and depth charges.

The big cruisers began lobbing big shells at their diminutive assailants from over six miles away. The Jamaica disposed of both four triple-6” gun turrets, as well as four faster-firing 4” dual purposes guns. Juneau bristled with six turrets each packing two 5” dual-purpose guns.

In Michael Hickey’s history Korean War, Midshipman Michael Muschamp of the Jamaica remembered the battle thusly:

“A very perturbed 18-year old donned clothes, anti-flash gear, and a tin hat in triple quick time. I made my way to my action station on the bridge…I soon saw what all the fuss was about.

There were six small craft, trapped between UN three warships and the shore, firing what appeared to be 20mm and 40mm cannon at Juneau and Jamaica. The two cruisers got the range of the craft and sank four within ten minutes. Another ran ashore in flames and the sixth escaped seaward.”

By the time the little boats had closed within two miles, torpedo boats No.24 had outright sunk by the powerful shells, and No.22 badly damaged. No.23 grounded itself ashore due to damage and was subsequently destroyed.

Both gunboats were destroyed as well, and two North Korean sailors captured.

By most accounts, the North Korean never launched any torpedoes. According to Muschamp, one of the rescued sailors when asked by an interrogator stated: “Oh, the Russians were going to teach us how to fire them [torpedoes] next week.”

Only boat No.21 escaped the engagement unscathed. Its captain, Kim Kun Ok, apparently reported sinking the American cruiser Baltimore—a victory which remains celebrated with a display (pictured here) in the Victorious War Museum in Pyongyang. This would have been quite a feat, as the Baltimore had been decommissioned four years earlier in 1946, and was at the time held in reserve in Washington state.

Bravado aside, the KPN subsequently decided to avoid directly engaging U.N. warships for the remainder of the conflict. However, it did continue using small boats for resupply and troop infiltration mission—most of which were subsequently sunk that July and August, including the ten KPN trawlers the motorboats had been escorting. 

Later on August 15, South Korean minesweeper YMS 503 intercepted a large North Korean convoy and sank 15 small boats, and captured 30.

As the UN solidified control of the seas surrounding the Sea of Japan, the gun-armed capital ships embarked on an extensive shore bombardment campaign. One tactic employed was to preemptively shell the cliffs overlooking coastal roads to create obstructing debris. The cruisers would then wait quietly at night with their running lights off for a North Korean convoy to arrive and dismount to clear the debris, before opening fire with a surprise salvo.

However, coastal bombardment missions came with their own risks. On July 8, Jamaica was bombarding a shore target when a remarkably well-aimed 3-inch shell fired by a coastal battery smacked into her superstructure, killing five artillerymen that had been manning the guns as well as one sailor. These were the first UK casualties of the Korean War.

The battle of Chumonchin Chan is today considered one of the six surface warfare engagements fought by the U.S. Navy since World War II, but the small size of the North Korean vessels has likely contributed to the engagement’s obscurity. 

Nonetheless, North Korea’s coastal fleet played an important role in the early days of the Korean War in projecting force against its southern neighbor. The vigorous counterattack mounted by ROK and UN naval forces likewise was vital in curtailing that threat—and laid the groundwork for the landing at Inchon that ejected Pyongyang’s troops from South Korea, and ultimately threatened the North in turn with invasion.

Sébastien Roblin holds a Master’s Degree in Conflict Resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing, and refugee resettlement in France and the United States. He currently writes on security and military history for War Is Boring. This article first appeared in September 2019.

Image: Flickr.