A recent Government Accountability Office (GAO) report found the Navy never fully assessed the costs and benefits of the Hybrid Electric Drive (HED) system program before shifting efforts to a different research program. The report noted the Navy did not conduct analysis to support the shift in research efforts.

The HED dates back to 2009, when the Secretary of the Navy established a goal to reduce energy consumption in Navy forces and two years later began a program to develop and install the HED system on Arleigh Burke-class DDG-51 Flight IIA destroyers (Defense Daily, Oct. 20, 2009).

The Arleigh Burke-class guided-missile destroyer USS Preble (DDG-88) transits the Indian Ocean in March 2018 while underway with the Theodore Roosevelt Carrier Strike Group for a regularly scheduled deployment in the U.S. 7th Fleet area of operations. (Photo: U.S. Navy)
The Arleigh Burke-class guided-missile destroyer USS Preble (DDG-88) transits the Indian Ocean in March 2018 while underway with the Theodore Roosevelt Carrier Strike Group for a regularly scheduled deployment in the U.S. 7th Fleet area of operations. (Photo: U.S. Navy)

The destroyers use one set of gas turbine engines to generate electricity, called generators, and another to propel the ship. In contrast, the HED draws surplus power from the electric generators to propel the ship.

“This allows the crew to turn off the engines typically used to propel the ship, thereby saving fuel,” according to the GAO’s Nov. 5 report, “Observations on the Navy’s Hybrid Electric Drive Program.”

Although the HED motor plus generators is more efficient than running both generators and engines, in this configuration the ship can only travel at a maximum speed of 11 knots, while the destroyers have a maximum speed of upwards of 30 knots when using the main engine. 11 knots was chosen as a limit because a significant percentage of the ship’s sea hours are spent at 11 knots or lower.

The report noted while the Navy has spent over $100 million on the development, purchase, and upgrade of six HED systems, they have only installed one on the USS Truxtun (DDG-103). The other systems are in storage while the Navy never bought the remaining 28 of a planned 38 total HEDs

This past July, the Navy said rather than install the remaining HEDs, it plans to use them for a new research effort, called the Propulsion Derived Ship Service (PDSS). PDSS aims to develop an electric motor that can move power to and from the ship electrical and propulsion systems rather than just from the electric system to the propulsion system as with HED.

In the FY ’19 Defense Authorization Bill Congress asked the Navy to submit a report on the HED installed on DDG-103 and requested GAO to review the report.  The GAO underscored while the Navy’s report, sent in January 2020, included some performance information, it “did not include a summary of the investment planned for the HED system.”

“Specifically, the report did not contain an assessment of the costs and benefits of the HED system or an assessment of the funding needed to execute the program. The Navy commissioned a business case analysis in 2013 and an update to this analysis would have included an assessment of the costs and benefits of the HED system,” GAO said.

The Navy said it did not include a summary of planned investment because the HED program was not included in the president’s FY ’20 budget request and cited a need for additional HED system data. However, GAO reported Congress appropriated $35 million for HED in 2020.

Service officials said they cannot use this funding to upgrade and install the five remaining HED before funding expires.

“Navy program officials told us that it will likely take over 3 years to upgrade the HED system, make changes to the ship’s software, and integrate the HED system into a ship’s maintenance planning. Further, Navy officials stated that they could not responsibly spend these funds to prepare for HED installations for which there was no planned funding,” GAO said.

The Navy’s 2020 report did provide some HED performance information, but not based on comprehensive testing. This covered performance of HED during an eight-month deployment in 2019. However, this was cut by five months due to a seal failure in the HED system that caused an oil leak.

“The Navy stated that the HED system could save up to 204 gallons of fuel per hour, or about 34 percent of the fuel usage, when the ship is traveling at low speeds. Further, the report stated that greater HED usage would enable a ship’s crew to stretch limited fuel budgets and remain at sea for longer durations,” the GAO said.

As of September, the Truxtun’s crew told GAO they used HED for 366 hours from March to July 2020 when it performed effectively and they saved about $329,000 in fuel. They also said HED was reliable and useful, allowing the ship to stay at sea for longer.

However, GAO reported the Navy’s report said “the HED performance information collected thus far cannot be used to draw conclusions about the HED’s overall performance. The Navy stated in this report that HED performance data was limited and insufficient to determine the overall performance of the system, although the Senate report had directed the Navy to conduct a comprehensive test and evaluation assessment of the HED installation on the USS Truxtun.”

Ultimately, the Navy report could only characterize HED performance based on 82 hours of operational data. Officials told GAO in April they do not know how many hours of testing is needed to understand system performance and reliability and they have no process to determine how much run-time is sufficient for conclusions.

“In contrast, a Navy test official told us that they have many ways to test systems that can provide timely information and comprehensive results without adding significant cost and time to the project. Without a comprehensive test and evaluation, the Navy does not have sufficient data to make an informed decision about the future of the HED program,” GAO said.

GAO noted they could not fully describe the Navy’s decision to suspend HED and use it for PDSS research because there was a lack of documentation on PDSS and information they gained from HED performance and benefits was different than the Navy’s justification.

In June, Navy officials told GAO they were shifting HED resources to the PDSS effort. “However, these officials also told us that they have no documentation associated with the PDSS effort—that is, there are no requirements or cost and schedule expectations.”

GAO argued while HED requirements officials told them there are several reasons to suspend the program, “the Navy is suspending the program without completing analysis that determines its costs, benefits, and performance, which is necessary to justify such a decision. Such analysis usually provides a foundation for these types of program decisions. Specifically, during the course of our review, we obtained information that differed from the rationale provided by Navy officials to justify suspending the HED program.”

GAO also said Navy officials said they have not determined how the service will use the five remaining HEDs to help the PDSS research effort.

“While Navy requirements officials stated that research into PDSS is necessary for supporting future weapon systems, they could not provide any documentation that illustrated the specific benefits of using the existing HED systems to aid in the PDSS research effort.”