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127mm Mk 45


Mk 45

A Mk 45 Mod 1 turret on an Arleigh Burke class destroyer. The 127mm shell is visible in front of the smoke.
Source: US Navy (Photographer’s Mate 2nd Class Felix Garza Jr) - © public domain

United States
Naval gun
Entered service
Mid 1970's
In service
1964 - 1970
United States - United Defense
1974 - present
United States - United Defense (now BAE Land Systems)
South Korea - WIA Corporation
Number produced
Over 210
KMK45 (South Korean production)
Notable users
United States
South Korea



The 127mm Mk 45 is a naval gun turret of US origin. It was developed in the 1960's by United Defense as a lighter alternative to the earlier Mk 42 turret. The Mk 45 is the smallest 127mm gun turret in the world and can be considered a direct competitor to the Italian 127mm Compatto. The Mk 45 is a lighter and easier to install design while the Compatto has a higher rate of fire and has more ammunition ready to fire. Both guns use the same US standard 127mm ammunition.


The Mk 45 is a single gun turret which is armed with the 127mm Mk 19 gun which was derived from the earlier Mk 18 that was used in the older Mk 42 turret. The Mk 45 is an unmanned turret with an automatic loader and a 20 round magazine below deck. Additional rounds are stored elsewhere in the ship and fed into the magazine using a feed chute. The gun is controlled using consoles below deck or in the command center. The latest development are a longer barrel and extended range guided munition (ERGM), the latter program was cancelled while the new barrel is in production.


The Mk 45 fires 127mm shells for use against shore targets, naval vessels and aircraft. The gun has a rate of fire of 16 to 20 rounds per minute. The maximum range is 23 km versus surface targets and the anti-aircraft range is quoted as 15 km. The latest Mk 45 design with longer barrel has a longer range and higher rate of fire. The ERGM round has a range of 117 km but was never fielded. Depending on the ship design the total ammunition load ranges between 475 and 680 rounds.


The Mk 45 is used on a wide range of modern US destroyers and cruisers. The Arleigh Burke class destroyers and Ticonderoga class cruisers are the main users of the Mk 45. Due to its ease of installation it was sold to various US allies for use on frigates and destroyers. The Mk 45 Mod 4 remains in production and has been exported as well.


Mk 45 Mod 1

The Mk 45 Mod 0, 1 and 2 have a L/52 gun and a round shaped turret.
Source: US Navy (Photographer's Mate 1st Class Robert R. McRill) - © public domain

54-caliber variants

The Mk 45 turret can be easily distinguished from the earlier Mk 42 turret by its shape and longer ordnance. The Mk 45 is one of the smallest 127mm gun turrets. The Mk 45 guns with original 54-caliber barrel can be identified by their round turret shapes since the Mod 4 uses an angled one.

Mk 45 Mod 0: Original production model with mechanical fuze setter and two piece barrel.
Mk 45 Mod 1: Improved Mod 0 with automatic fuze setter and unitary barrel.
Mk 45 Mod 2: Export version of US Navy Mod 1.

Mk 45 Mod 4

The Mk 45 Mod 4 turret has a longer L/62 gun and an angular shape turret.
Source: US Navy (Mass Communication Specialist 2nd Class Bryan Reckard) - © public domain

62-caliber Mod 4

The Mk 45 Mod 4 is a much improved Mk 45 turret. The Mod 4 has a low radar cross section turret design which is not as rounded as the original Mk 45. A longer 62-caliber gun is fitted which results in a 20 percent longer range for standard ammunition and extended range guided munition (ERGM) may be fired, although the ERGM program was cancelled in 2008. The rate of fire has been increased and for short bursts it is even doubled. The ammunition loading system below deck remains the same.


Facts Mk 45 Mod 0 Mk 45 Mod 2 Mk 45 Mod 4
United States
Naval gun turret
127mm 54-caliber
Rate of fire
16 to 20 rpm
23 km vs surface targets
15 km vs aircraft
Muzzle velocity
762 m/s
Feed mechanism
Automatic loader
20 rounds in loading system, single feed chute
-170° to +170° at 30°/s
-15° to +65° at 20°/s
3 or 6
24.3 t empty


Related articles

127mm Mk 42

The Mk 45 was designed as a more modern alternative to the Mk 42 naval gun turret. Both systems use the same range of 127mm ammunition.

127mm Compatto

The Italian Compatto is a competitor to the Mk 45. The Compatto has a slightly better performance and is a larger and more complex system.