Najin class Frigate (1973)

North Korean Navy – Missile Frigates 1973-Today: Two ships, status unknown.

The Najin class (NATO designation) are known by Western intel since 1971 when construction was spotted by satellite. They are among the most foggy North Korean Vessels while at the same time, the largest in the Korean Navy until the 5000t Choe Hyon-class destroyer as of 2025, designed to replace them. NATO assumed the pennant numbers of the first two (and likely the only ones) pennants #531 and #631. According to Jane’s Fighting Ships 1983-84, four were built, but nowadays, many authors agrees only two, with names unknown. Status unknown today, albeit back in 2014 Nknews, stated one was undergoing a modernization in 2014 at Namp’o, as missile ship with new electronics installed, 30mm automated turrets and two Kh-35 missile racks SSMs and becoming the fleet’s flagship since.

Design of the class

As all Vessels of the “Hermit Kingdom”, the Najin class are known by Western intel since decades, as they became the centrepiece of a largely green water Navy. Analysts were stuck to rare declarations (none about their launching or development, for example) and their appearance over time, seen through blurry satellite photos. These ships bear a striking resemblance to Soviet Kola-class frigates, but most agree they are unrelated to any Soviet or Chinese vessel while being built in the 1970s. It is generally estimated their construction started in 1971 according to satellite intel, and completed likely in 1973 for the first two, and 1979 for the remaining two if indeed they were not the same vessels. No photos ever showed more than two vessels at the same time.
It should be added that the Soviet Kola class also inspired the first Chinese frigates, which from there all sported the same basic flush deck, low freeboard hull form. Since North Korea lacked the technology to create gas turbines or even modern steam turbines, they are known to be equipped with simpler diesel, ensuring better range for long patrols along the coastline, at the expense of speed.

The NATO name could be derived from the Yard in which they were built at Nanjin. The space between funnels was occupied by a bank of torpedo tubes but in the 1980s they were shown with what seemed to be two SS-N-2A launchers, converting these as the first North Korean missile frigates. These launchers are believed the same as in the OSA I class boats with Chinese-derived P-15 Termit (NATO Styx) missile, but the installation is rather crude and apparently dangerous. The main gunnery is believed dating back to WW2 or the 1950s, Soviet origin too, and largely obsolete by the 1980s standards due to their allegedly poor fire control. The electronics are also from the early generation, the exception to the recognized “Drum Tilt” set from 1961.
In 2023, these two frigates remain active with North Korea’s navy after a service of 50 years after commission.

Hull and general design

For what NATO estimated from satellite, since no data was published, they were displacing an estimated 1,600 long tons (1,600 t) for an overall length on 328 ft (100 m), a beam of 32.8 ft (10 m) and a draught of 8.9 ft (2.7 m). The Complement, for what was known of the different systems installed and Kola-class and Chinese equivalent frigates, around 180 officers and men.
The design showed a slab-sided hull with transom stern aft, gradual curves with a prow 2.5 times taller than the poop, pointy and clipper-like with some flare. The overall outlook is conventional with two deck guns under shields (not full turrets as the back is open), and a low structure supporting two 57 mm AA open mounts fore and aft in “superfiring” positions.

Then came the superstructure, with a 2-storer tall bridge, enclosed but with wings and an open bridge atop, and sensors, then a main derrick mast supporting extra sensors, partly built around the fore funnel, small and raked, then a CIWS, a gap on which was initially located the amidship torpedo tube bank and the rear structure with a smaller derrick support for the main Drum Tilt radar, the rear funnel, lower and still raked but of the same time and a rear structure and CIWS. There are a few portholes on the forward hull up to the level of “A” AA mount, two at the stern. Six twin 25mm lighter AA gun positions, shielded are seen abaft the bridge, first funnel and second funnel covering both sides. Two ASW grenade racked are located at the poop, long enough to carry 8 each.

Powerplant

The Najin class propulsion had been described as resting on two diesels only of 7500 hp each for a total output of 15,000 bhp (11,000 kW) on 2 shafts. Their origin is unknown, but they are likely based on civilian merchant models. The North Koreans had indeed a sizeable merchant navy inherited in part from Japanese occupation, despite part of it was sunk in the Korean war. Others could have been purchased later from the Soviet Union and/or China to keep the fleet updated. Merchant Marine diesels are known to be enduring, reliable, with a lot of torque but not tailored for blazing top speeds, so NATO analysts by crossing the size an estimated tonnage the Najin class had an estimated top speed of 26 knots (48 km/h; 30 mph) allowed by the hull design, quite efficient. Other calculations led to believe her range around 4,000 nmi (7,400 km; 4,600 mi) at 14 knots (26 km/h; 16 mph).

Armament

100mm/56

These are likely Chinese 100 mm/56 (3.9″) Type 79. They fire a complete 61.7 lbs. (28 kg) round, AA (3 types) or HE m1928 and star shell. They are identical to those of the Kola class Frigate and their Chinese equivalent, with each gun weighting 2.424 tons (2.463 mt). Allegedly capable of 25 rounds per minute, they have a Max range of 24,323 yards (22,241 m) and Ceiling of 32,800 feet (10,000 m) for a Muzzle Velocity of 3,004 fps (915 mps) for the Chinese Type 79 standard AA round.
In China, these guns equipped the Luhai, Luhu, Jiangwei and Jianghu classes.

57mm/70 AK-257

Converted from ZIF-31 L/70 57mm (Type 66/76) land cannons. Usually associated with the Yakhond (Hawk Screech) radar. They are more likely their Chinese variant called the Type 66 unless they were of the later water-cooled derivative known Type 76. They generally fired a Tracer FRAG UOP-281 or UOP-281U at 100-150 rounds per minute if liquid-cooled, up to 9,210 yards (8,420 m) in range, visual for guidance and hand-manned. Their open-top enabled 90° elevation but made them vulnerable to strafing.

Light AA

These ships entered service allegedly with two twin 25mm AA and four twin 14.5mm AA at the start in 1973. Both the 25mm and 14.5 mm DsHk were likely Chinese copies. The 25 mm/60 Type 61 for example was installed on either turreted or shielded tandem mounts, typically (one on top of the other). It seems, according to the only 1993 close enough photo above, they were enclosed turrets, looking like singles as the lower barrel was difficult to see.
The 25mm Type 61 fires a 1.42-1.48 lbs. (0.644-0.672 kg) shell depending on the type, FRAG, AP Tracer or the Chinese HE-I-T: 0.62 lbs. (0.282 kg) coming with a 0.25 lbs. (11.5 g) RDX charge, 11.5 in (29.2 cm) long. Muzzle Velocity is 2,950 fps (900 mps) with 270-300 rpm effective, 2,625-3,050 yards (2,400 – 2,800 m) range or 5,500 feet (1,700 m) ceiling.
The 14.5 mm could be either the Chinese Type 58 heavy machine gun, a KPV copy. In short, 600 rpm, mv 1,005 m/s (3,297 ft/s), effective range 3,000 m (9,800 ft).

CIWS

Later this was upgraded to four 30 mm (1 in)/66 (2 twin or two sextuple tubes) AK-630 CIWS perhaps take from OSA class FACs.
In complement, the ships retained their twelve 25 mm (0.98 in) machine guns in six twin mounts. By the 1990s, such armament was hopelessly obsolete, but still potent in a gunboat role against South Korean patrol vessels.
It seems also that on the other ship in class, in place of the aft 57mm as was present are two AK-230 30mm turrets, side by side. Where the aft AK-230 used to be in the 90s, there is now a MANPAD-based SAM launcher, as well as 6x 82mm chaff/smoke launchers next to it.

SS-N-2a Styx SSMs

Installed in place of the amidship TT bank (type is unknown) in 1984-85*, two Kh-35 missile racks on either side of the rear structure, facing forward, their path unobstructed but passing very close to a 25 mm AA mount and the whole bridge, so a hypothetical launch was to be quite dangerous if anything went awry. There seems to be a gantry between the tow launcher where the TT banks were located, probably for reloading, with 8 missiles in stores total.
The P-15 Termit (NATO SS-N-2a Styx) was copied by China, notably for its Hoku class FACs as the HY-2 Missile.
The Shang You or SY-series and Hai Ying or HY-series (‘Sea Eagle’) were early Chinese anti-ship cruise missiles derived from the Soviet P-15 Termit. NATO designation is Silkworm.
Dimensions: 7.48 m, Diameter 0.76 m, Wingspan: 2.4 m.
Launch weight: 2,998 kg
Warhead: 513 kg, shaped charge high-explosive
Propulsion: Liquid rocket engine and one solid rocket booster
Speed: Mach 0.8, Range 200 km, altitude below 20 m
Guidance: Inertial + active conical scanning terminal guidance radar, single-shot hit probability: 90%
It seems the torpedo tubes were installed back, two launchers fitted on either side of the aft 100mm turret, likely Soviet Type 53 (possibly 53-38).
In the 2010s, they were replaced by the SS-N-25 Switchblade (two quad Kumsong-3 SSM). The Kumsong-3 (KN-19) are a Reported North Korean copy of the Kh-35U. Kumsong-3 is a North Korean domestic variant/clone of Kh-35 likely based on Kh-35U due to range. Demonstrated range in 8 June 2017 test is 240 km.

RBU-1000 ASWRL

Smerch-3 is a 300 mm calibre Russian anti-submarine rocket launcher of small size. Weight: 2900 kg, 2165 x 2000 x 2030 mm, traverse rate 30 °/sec, Crew 4.
Fires the 1800 mm 195 kg RGB-10 (РГБ-10) rocket for a range of 100-1000 m. Warhead:100 kg, sink rate 11.8 m/s, max depth 450 m. They were removed at an unknown date

ASW and Mines

The Najin 2 DCR, 2 ASWM, mines. Not any more information. The mines were never spotted on any photos, and the DCT are difficult to spot.

Sensors

Navypedia states they were originally equipped with the type 351, type 352, Fut-N, Rangout radars, Tamir-10 sonar. For active protection, they were fitted at some point with the type 923-1 ECM suite, and six 6-round decoy Rocket Launchers.
Air search: “Square Tie” or “Slim Net” radar.
Surface search: “Pot Head” radar (Reya) and “Skin Head” (Zarnitsa)
Navigation: “Pot Drum” radar ()
Fire control: “Drum Tilt” (MR-104 Rys)
Sonar “Stag horn”, hull-mounted active search/attack model.

Update Chonology

Early of mid-1980s, removal of their amidship triple TT bank 533mm TT and installation of their single twin P-15 Termit SSM launcher plus 8 reloads.
In the late 1980s, removal of their twin P-15 Termit SSM, and four twin 14.5mm/89 AA HMGs and four 5-tube RBU-1200 ASWRL, as well as two 2 DCT for two single P-15 Termit SSM, two twin 30mm/71 AK-230 CIWS and installation of the MR-104 Rys’ radar (Drum Tilt).
By the late 2010s these P-15 Termit SSM were removed and replaced by two quad Kumsong-3 SSM (8 Kumsong-3 in store) whereas #591 saw the removal of her four twin 30mm/71 AK-230 CIWS.

Profile (navypedia)

⚙ Najin class specifications
Displacement	1,600 long tons (1,600 t)[
Dimensions	328 x 32.8 x 8.9 ft (100 x 10 x 2.7 m)
Propulsion	2 shafts diesels 15,000 bhp (11,000 kW)
Speed	26 knots (48 km/h; 30 mph)
Range	4,000 nmi (7,400 km; 4,600 mi) at 14 knots (26 km/h; 16 mph)
Armament	2×100 mm /56, 2×2 57 mm, 30 mm/66, 12×25 mm, 2x RBU 1200, 2 CDT, 2 DCR, 30 mines
Protection	6×6 Decoy Launcher, ECM
Sensors	See notes
Crew	180

Current Status

Since the last refit and modernizaton in 2014 it is likely that at least one ship is fully operational until planned replacement by the new Choen Yon class. The Najin class frigates had been the largest most capable as well as longest lasting surface combatants of North Korea and most analysts assumed there is one for each coast, Hull number 531 on the east coast, hull number 631 being the west coast. Rare sightings and photos have been of #531 alone plus a recent footage of the same (pics). Given the secrecy surrounding the assets of this Navy, it is likelt we have to assume only #531 is still operational and her sister 631 had been replaced by the current Choe Hyon, albeit the fully operational status of the latter is unknown.

Potential Replacement: The Choe Hyon class destroyer

Official photo from NK TV, reddit
Lambasted in world’s medias for the calamitous launch of Kang Kon in May 2025, this class is the first modern missile destroyer class of the North Korean Navy and designated replacement of the now obsolete Najin class. The Choe Hyon-class destroyer (《최현》급다목적구축함) were unveiled by the Korean People’s Army on 30 December 2024 with a second ship, Kang Kon, restored to upright position and launched again on 12 June 2025. Three are on order according to the current Five-Year Plan for January 2026. However Kim Jong Un approved a plan to build two more of this class in 2026. Nampo Shipyard is working on the third ship to be launched for the 81st Party Foundation Day in October 2026. #53 was indeed laid down on 21 July on 21 July this year.

Unlike for the Najin class, analysts are unsure of what their systems are due to the sleathy and fuller shapes of the ships that can hide many unknown systems. For what is visible through, this class ought to be a significant step into modernism as the class are first surface vessels in the Korean People’s Nav equipped with a phased array radar an vertical launching system (VLS). As for now, these estimated 5000t, 145 meters long vessels are armed with a 127 mm or 130 mm naval gun, a Pantsir-ME CIWS, two 30 mm AK-630 CIWS ad substantial 74 × VLS cells, four quadruple anti-ship missile launchers and four quad Bulsae-4 launchers and two twin 533 mm (21.0 in) DTA-53 torpedo launchers plus an helicopter or UAV with a flight deck, however the “hangar” is topped by a VLS, which could be a bogus one. We will go back on this class in a few years for deeper analysis as more is unveiled.

Gallery

Colorized photo of the well-known close shot now CC (facebook).

src reddit