After two unscheduled stops for repairs, the USS Zumwalt (DDG-1000), the US Navy's new stealthy all-electric-powered destroyer, arrived at its new home port in San Diego on December 8. The ship also brought along new details about the source of its engineering woes. Zumwalt's propulsion issues, which caused the ship to have engineering failures off Norfolk, Virginia, and while transiting the Panama Canal, were caused by seawater getting into the ship's lubrication system for its huge electric motors.

US Naval Institute News' Sam LaGrone reports that the root cause of the engine failures was seawater contamination in the lube oil for the bearings of Zumwalt's Advanced Induction Motors. Rather than being driven by dedicated gas turbine engines, the Zumwalt's motors are powered by electricity from the gas turbine generators that also power the rest of the ship. The power plant is the first of its kind in a Navy ship, and it could generate enough power to allow Zumwalt to be later refitted with directed energy weapons or electromagnetic railguns.

The seawater apparently got into the motor bearings via a faulty lubrication oil chiller. The chiller uses water drawn in from outside the ship to prevent the oil around the motor's bearings from breaking down and to cool the bearings themselves while they're under load. The cause of the leaks has yet to be determined.

Now that the ship is in San Diego, the installation, activation, and certification of Zumwalt's weapons systems will be completed over the next few months. The ship is not expected to enter full service in the fleet until 2018. There's still some question about just how the Navy will certify the Zumwalt's gun, as the special shells the Advanced Gun System was supposed to fire have been deemed too expensive by the Navy, at $800,000 per round.