US destroyer deployed for Iran operations gets its 5-inch gun back after two years

The U.S. Navy has restored the 5-inch gun aboard the guided-missile destroyer USS Donald Cook after a stubborn fault kept the weapon out of service for two years. The repair returned the ship’s Mk 45 gun to full naval gunfire support readiness during a deployment supporting ongoing operations involving Iran.

The Mid-Atlantic Regional Maintenance Center (MARMC) disclosed the fix on Oct. 1. Navy technicians traced the malfunction to a failed fire control interface circuit card that stopped a required 25-volt direct-current signal from reaching the gun system. A later live-fire exercise produced what the Navy called highly satisfactory results.

A gun sidelined two years

Donald Cook carries the Mk 45 Mod 2 5-inch (127 mm), 54-caliber gun, which can engage surface and land targets. With conventional ammunition it reaches about 13 nautical miles (15 miles, or 24 kilometers) and fires 16 to 20 rounds per minute.

The casualty did not leave the destroyer defenseless. The ship kept its Mk 41 Vertical Launching System, which fires Standard Missiles, Tomahawk cruise missiles and anti-submarine rockets, along with Phalanx close-in weapon systems and torpedoes. Still, the failure removed a distinct rapid-fire capability from its arsenal for two years.

Thinking beyond the manual

Earlier troubleshooting repeatedly focused on components flagged in standard technical documentation without fixing the problem, so the latest team had to look beyond the normal diagnostic sequence. MARMC technicians Brian Hall and Adam Harlan of the Surface Fire Control/Guns Branch disabled the compensation circuit inside the gun’s Electronic Servo Control Unit.

The gun immediately returned to its commanded position, which let them follow the missing electrical signal back to the defective card.

Logistics across oceans

Getting the specialists aboard took an unusually complex effort. Hall and Harlan traveled from Norfolk through Europe and Djibouti, then flew about seven hours aboard a CMV-22B Osprey to an aircraft carrier in the region. The tiltrotor refueled in the air three times during the flight. An MH-60R Seahawk carried them the rest of the way after heavy seas complicated an earlier attempt to reach Donald Cook.

Work continued while the ship stayed underway. Technicians worked around the destroyer’s schedule and weather that at times limited access to exposed equipment, since sea spray can damage electronics.

Once the faulty card was identified, a replacement had to reach a warship in the Indian Ocean. MARMC personnel in Norfolk expedited the part commercially to Singapore, and Donald Cook’s supply team arranged onward movement through Diego Garcia. The card arrived in 12 days, compared with more than a month that MARMC says the process can normally take for an underway ship in the region.

What the fix means

After the card was installed and secondary electrical faults were resolved, the crew conducted a live-fire event that verified the repair. That firing was a post-repair check, not an engagement of an enemy target.

The Mk 45 does not replace the destroyer’s missile-based strike and air-defense systems, but it widens the commander’s options for surface warfare and gunfire support. That matters on a deployment that the Navy says supports ongoing operations involving Iran, where surface combatants may need several layers of offensive and defensive capability at once.