A vintage deck gun system that was once a staple of the U.S. Navy and Coast Guard has quietly fired its final shots.
Designed by the famed munitions firm of OTO Melara of La Spezia, Italy, and marketed from 1963 onward as the 76/62C Compact, the remote-controlled 76mm (3-inch) gun with its characteristic bubble dome was an immediate hit with NATO and Western fleets, eventually seeing service with 60 nations.
West German Type 148 missile boats show their 76mm OTO guns during a visit to the UK, in 1977
The reason it was so popular was that using aluminum alloys, a water-cooled gun barrel, and an automatic loader with an 80-round magazine, it delivered much better performance than any manned 3-inch gun mount in service at the time while weighing much less. Guided by the ship’s onboard radar and fire control system, it could engage air targets as high as 13,000 feet and surface targets out to 20,000 yards.
The 76/62 designation comes from the bore (76mm) and barrel length (62 caliber), the latter figure denoting a 4,724mm long barrel, which translates to 15.5 feet.
The 76/62C Compact, seen in its components from a 1980 U.S. Navy training publication:
Note the gun control panel which was mounted in the ammunition handling room below deck under the mount. The mount captain fired the gun from the panel while two ammunition loaders stood by to reload the magazine.
A look under the hood so to speak, showing off the details of the gun itself and its magazine.
The mag used two concentric rings of shells, each holding 35 rounds, with a hydraulic motor rotating the screw feeder– which held another six rounds not unlike that of a common “six-shooter” revolver. Together with the four rounds held in the loader drum, the gun held 80 shells, which could be expended in just under one minute.
A view of the magazine rings of the MK-75 gun aboard USCGC Mohawk (WMEC 913) while underway in the Atlantic Ocean, Sept. 1, 2022. (U.S. Coast Guard photo by Petty Officer 3rd Class Jessica Fontenette)
The types of “war shot” rounds in U.S. service included High Explosive Point Detonating (HE-PD), High Explosive Infrared (HE-IR), Variable Time Non-fragmenting (VT-NF), High Explosive Variable Time (HE-VT), and High Explosive Radio Frequency proximity (HE-RF).
Exercise and training shells included the Blind-Loaded and Plugged (BL&P) round with a live round that had an inert projectile while wholly inert rammable and non-rammable dummy and gauging rounds were also available.
Crew load 76mm rounds into the magazine of the MK-75 gun aboard USCGC Mohawk (WMEC 913) while underway in the Atlantic Ocean, Sept. 1, 2022. HE-PD rounds can be seen in the outer ring and blue-colored BLP target rounds are peeking out of the inner ring. (U.S. Coast Guard photo by Petty Officer 3rd Class Jessica Fontenette)
The gun control panel below-deck under the mount, complete with its view of the magazine rings. Seen on the USCGC Midgett (WHEC 721) in June 1999. USCG photo by PA2 Alice Sennott
Shells were brought on and off the packed in grey shipping containers, loaded old-school via chain gangs.
Sailors aboard the Oliver Hazard Perry-class guided-missile frigate USS Rodney M. Davis (FFG 60) move 76mm rounds during an ammunition onload. Rodney M. Davis, based out of Everett, Wash., is on patrol in the 7th Fleet area of responsibility supporting security and stability in the Indo-Asia-Pacific region. (U.S. Navy photo by Mass Communication Specialist 3rd Class Derek A. Harkins/Released)
For a great look at the inner guts of the 76/62C Compact, check out this short video from the German Navy, which has used the gun since 1965. Don’t worry if your German is rusty, the video speaks for itself.
With the U.S. Navy opting to mount a smaller 3-inch gun on its planned Oliver Hazard Perry-class frigates in the 1970s– a big change from the manned 5-inch guns mounted on the Knox-class frigates that preceded them– the Pentagon went with the Italian “robot gun” design.
A destroyer escort, USS Talbot (DEG-4), in late 1974 had an Italian-produced 76/62C Compact installed on her bow forward of the superstructure in place of the ship’s original 5-inch manned mount which used a design that dated to World War II.
USS Talbot seen circa 1974-75 with an OTO Melara 76/62C Compact installed. (Photos: U.S. Navy History and Heritage Command)
The Naval Systems Division of the FMC Corporation in 1975 won the U.S. contract to build the 76/62C Compact in Pennsylvania under license from OTO Melara and delivered the first American-built model in August 1978. The Navy, which designated the gun the MK 75, went on to install them in 51 Oliver Hazard Perry-class frigates built between 1975 and 1989, along with six Pegasus-class hydrofoil fast attack craft and on the Coast Guard’s 13 new Bear-class cutters that were constructed in the same era.
Likewise, when the Coast Guard’s 12 Vietnam-era Hamilton-class cutters were modernized starting in 1987, they received the MK 75 to replace their outdated 5-inch mounts. The guns were also installed on a series of warships built in the U.S. for overseas customers (Israel, Egypt, Australia, et.al).
The frigates carried the MK 75 atop their superstructure as the bow, the traditional location, was occupied by a missile launcher and its below-deck magazine.
October 2002. USS Sides (FFG 14) fires her 76mm dual-purpose gun at ex-USS Towers (DDG 9) during a SINKEX near San Diego. (Photo: U.S. Navy)
May 2011. The Oliver Hazard Perry-class guided-missile frigate USS Thach (FFG 43) fires its MK-75 76mm mounted gun while underway off the coast of Brazil. (Photo: U.S. Navy)
August 2014. The Oliver Hazard Perry-class guided-missile frigate USS Rodney M. Davis (FFG 60) conducts a live-fire exercise of its MK 75 76mm/62 caliber gun. (Photo: U.S. Navy)
One of the frigates, USS Simpson (FFG-56), part of Surface Action Group Charlie, had the first combat use of the MK 75 in U.S. service when, in April 1988, used the gun to destroy Iranian naval and intelligence facilities on the Sirri oil platform during Operation Praying Mantis.
Another frigate, USS Nicholas (FFG-47) used her MK 75 during Desert Storm in January 1991 to clear Iraqi troops placed on nine oil platforms in the northern Persian Gulf off of occupied Kuwait. As reported at the time, the frigate “fired three shots at each platform to set the range, followed by about 20 rounds of high-explosive shells, ‘for effect.’ The effect was to demolish quickly all the remaining bunkers.”
The speedy hydrofoils, meanwhile, wore their MK 75 as a hood ornament.
As did the Coast Guard cutters.
Coast Guard Cutter Harriet Lane firing a commemorative shot on 30 May 2019 to honor the 158th anniversary of its namesake’s action near Fort Sumter, South Carolina. (Photo: USCG)
The water-cooled barrel, using salt water during the firing process and a freshwater flush from the ship’s onboard supply after the firing ceased, led to often extreme muzzle shots with the intersection of steam and propellant.
The crew of Coast Guard Cutter Northland conducts a live firing of the MK 75 76mm weapons system while underway, on September 20, 2020, in the Atlantic Ocean. (Photo: USCG)
March 2000. The Coast Guard Cutter Tampa’s 76mm gun blasts a projectile at a moving target during live-fire exercises. Participants took turns firing at “robo-ski,” a small, remote-controlled jet ski. Tampa gunners hit the target every time. USCG Photo by ET3 Shane Taylor.
The gun uses a saltwater cooling system and a freshwater cleaning run after firing concludes, seen here on USCGC Escanaba in 2028.
All things come to an end
However, there has been a slow-motion end to this story that started with the retirement of the hydrofoils in 1993, and the frigates losing their MK 75s by 2015 in a series of refits. This left the Navy, who “owns” the installed weapons on Coast Guard cutters, still on the hook for logistics contracts with BAE systems and OTO Melara (now Leonardo) for parts and support.
Those days are gone as the 76/62C is out of production both in the U.S. and Italy, with Leonardo replacing the system in its catalog with the faster-firing (though still with only an 80-round ready magazine) and more stealthy 76/62 Super Rapid (SR) Gun Mount.
Eventually, the Ordnance Shop at the Coast Guard yard took ownership of the MK 75 program and was even tapped to support the guns on frigates and cutters transferred overseas.
Since then, the Hamilton class has all retired and has been transferred overseas and now the Bear class cutters are in the process of being stripped of their MK 75s during refits, and replaced by smaller (albeit currently produced) MK 38 25mm guns. Overseas allies are similarly phasing out the gun.
This brings us to the coda of the Bear-class USCGC Mohawk (WMEC 913) firing her MK 75 for the last time this summer, an event that was held during a gunnery exercise in the Florida Straits. The service said in a press release this week that it was a “significant historical event” as Mohawk was “the last in its class to fire the onboard Mk 75 gun weapon system.”
Coast Guard Cutter Mohawk’s (WMEC 613) Mk 75 weapon system fires, Aug. 16, 2024, during a gunnery exercise in the Florida Straits. Mohawk was the last Famous-class medium endurance cutter to fire the onboard Mk 75 mm gun weapon system as large caliber weapon systems onboard these cutters are being modernized for the service life extension program. (U.S. Coast Guard photo by Ensign Brian Morel)
Perhaps once the mount is phased out for good, the USS Aries Museum, the only preserved U.S. Navy hydrofoil, can pick up one of the old MK 75s to help complete her Cold War profile.
If the Oliver Hazard Perry Shipyard on Lake Erie ever gets their retired Perry from the Navy, they could showcase one as well.