Groton - USS North Dakota is out to sea, but an investigation into third-party vendor issues that caused the nuclear attack submarine's commissioning to be delayed is ongoing.

The Navy postponed North Dakota's commissioning, originally set for the end of May, to Oct. 25 because of issues related to vendor components and additional design and certification work required on the submarine's redesigned bow.

North Dakota is the first submarine to have the redesign with a new sonar array and two larger payload tubes instead of 12 individual, vertical-launch missile tubes.

Colleen O'Rourke, a spokeswoman for Naval Sea Systems Command, said the investigation into the third-party vendor began in April and is led by the shipbuilders, Electric Boat and Huntington Ingalls Industries, in conjunction with the Navy. The name of the vendor is not being released while the investigation is underway.

The issues led North Dakota to be drydocked on April 21 to allow for inspection of parts with suspected deficiencies, including stern planes and rudder rams; retractable bow plane cylinders; hydraulic accumulators; high-pressure air-charging manifolds; torpedo tube interlocks and shaft/link assemblies; weapons shipping and handling mechanisms; and other parts.

EB inspected those outboard and inboard components and corrected all mandatory deficiencies, according to an earlier statement provided to The Day from Capt. Darlene Grasdock, supervisor of shipbuilding in Groton.

As for the additional design and certification work, Naval Sea Systems Command and EB examined operational scenarios and casualty situations and eventually concluded that North Dakota was satisfactory for at-sea operations. All inboard and outboard components whose failure might cause major mission impact, major injury, loss of ship or loss of life were inspected and all required repairs were completed, according to the earlier statement from Grasdock. North Dakota was certified for sea trials on July 25 and successfully completed those trials in mid-August.

Despite the pending investigation, the vendor is still working on Navy contracts.

"The vendor is still working on select components with 100 percent oversight/work controls from the shipbuilders. The extremely critical component work is being removed from the vendor and taken in-house with the shipbuilders," O'Rourke said in an email.

EB led the redesign of the submarine and, despite the redesign issues, delivered North Dakota to the Navy two days early and under cost by more than $30 million, with the highest-quality score to date, as measured by the Navy Board of Inspection and Survey.

Kurt Hesch, vice president of EB and Virginia-class program manager, said in a statement that the sub builder "continues to work closely with the Navy on this matter. Because the investigation is ongoing, however, we would prefer not to expand on the Navy's statement."

j.bergman@theday.com

Twitter: @JuliaSBergman