A repair bill of an estimated $23 million and months out of action. That’s the cost to U.S. taxpayers and the Navy after the four-year-old littoral combat ship USS Forth Worth tried to operate its propulsion system without enough oil in January. The Navy announced Wednesday that the $360 million vessel would make a six-week-long journey this summer from Singapore, where it has been tied up since the incident, to San Diego for repairs to its combining gears, the hardware that transfers power from the ship’s diesel and gas turbine engines to its water-jet propulsion system. “The casualty occurred due to an apparent failure to follow procedures during an operational test of the port and starboard main propulsion diesel engines,” said the Pacific Fleet in Pearl Harbor, Hawaii, in a statement issued earlier this year. “During start up of the main propulsion diesel engines, lube oil was not properly supplied to the ship’s combining gears as required by ship’s operating procedures,” said Lt. Cmdr. Timothy Hawkins, a Navy spokesman. “The insufficient flow of lube oil resulted in high temperature alarms on the port and starboard combining gears.” The Navy’s $23 million cost estimate for the USS Fort Worth covers already underway maintenance, transiting from Singapore to San Diego and scheduled repairs and maintenance once the ship reaches its home port, according to Hawkins. “Preparations are expected to take several months to complete necessary inspections, conduct lube oil system flushes and configure the engineering plant for safe operations,” a Pacific Fleet statement said. The 388-foot, 3,400-ton Fort Worth will make the 8,900-mile trans-Pacific voyage using just the power from the gas turbine engines, meaning it will be slower and require several more refueling and supply stops that would normally be the case, the Navy said. Putting as bright a face as it could on the incident, the Navy said the Fort Worth’s repair time in San Diego would coincide with a planned maintenance period in its home port. The incident cost the then-commander of the Fort Worth, Cmdr. Michael L. Atwell, his job in late March when the Navy announced Atwell was being reassigned to LCS squadron duties in San Diego. “Sufficient findings of facts emerged during the investigation to warrant the relief of the commanding officer,” the Pacific Fleet said in a statement at the time. The mechanical mishap on the Fort Worth came shortly after a similar mistake on its sister ship, the USS Milwaukee, which broke down in the Atlantic Ocean on December 10, less than a month after it was commissioned. The ship had to be towed 40 miles to Joint Expeditionary Base Little Creek-Fort Story in Virginia. The Navy said at the time that metallic debris was found in filter systems in the ship, causing a loss of pressure in lubricant to gears that transfer power from the ship’s diesel and gas turbine engines to its water jet propulsion system. Navy officials later explained what happened in an email to CNN. The Milwaukee “is designed to operate with gas turbine and diesel engines, which can operate in tandem or independently,” Navy Lt. Rebecca Haggard said. “In the case of Milwaukee, when switching from one system to the other, a clutch failed to disengage as designed. Instead, the clutch remained spinning and some of the clutch gears were damaged.” The Milwaukee has undergone repairs and in late February steamed from Virginia to Mayport, Florida, where the Navy said it would take on additional equipment for testing this spring before proceeding to its home port in San Diego. The Navy’s littoral combat ships come in two variants: the monohull and the trimaran. The Fort Worth and Milwaukee are monohulls. With a draft of between 14 and 15 feet and a speed of 40 knots, the ships are designed to operate in littoral environments, or shallower coastal areas.