WASHINGTON -- In September 2012, the Navy began in-water work at Naval Base Kitsap Bangor to build an explosives-handling wharf, a $650 million project anti-nuclear activists criticized as an unneeded vestige of the Cold War.

Unknown to the public at the time, however, was that plans for the new wharf had proceeded despite opposition from within the Pentagon.

An independent agency, the Department of Defense Explosives Safety Board, had refused to grant a permit for the project, citing concerns about how close it would be to an existing wharf that handles Trident missiles carrying nuclear warheads.

Instead, the Navy obtained what's called a secretarial certification. That allowed the service to assume safety risks for the second wharf on its own, clearing the regulatory hurdle for construction.

The Navy's omission of the safety board's misgivings has become a key part of a long-running legal fight by Ground Zero Center for Nonviolent Action, a Poulsbo, Wash.-based anti-nuclear group. Ground Zero has accused the Navy of withholding facts that would have fully informed the public of the second wharf's potential dangers, as required under the National Environmental Policy Act.

Among other things, Ground Zero contends the Navy's final environmental-impact statement left out crucial information, such as that the two wharves violate the Pentagon's minimum distance for separating explosives. The Navy also did not disclose that the safety board called for a study, which the Navy chose not to pursue, to show that an accident at one site would not trigger an explosion at the adjacent wharf.

"Our goal is for the public to understand the impact of this project," said Kathy George, an attorney with Harrison-Benis in Seattle who is representing Ground Zero.

The naval base is nestled between Poulsbo and Silverdale, Wash., on Hood Canal, just a few miles from population centers. It's the home port for eight Trident nuclear submarines, whose Trident II D5 missiles are being upgraded to extend their service.

The existing wharf was built during the 1970s, and the Navy said maintenance and other work on the aging structure means it's available only 200 days a year; the Navy says missile-upgrade operations demand 400 days of wharf access, which is only possible with a second wharf.

Ground Zero is seeking to force the Navy to conduct a new environmental-impact review. That may or may not halt the wharf construction. After 18 months of legal volleying, a decision by U.S. District Court Judge Ronald Leighton in Tacoma, Wash., is pending.

The explosives danger with the Trident missiles primarily involves the volatile rocket-motor propellant. Experts say such accidents are unlikely to cause a nuclear detonation. But a conventional explosion of the propellant could disperse the radioactive plutonium within the warheads across Puget Sound, according to a 1994 paper on Trident nuclear-weapons safety written by experts at Stanford University and the U.S. State Department.

Citing the continuing litigation, Don Rochon, a Navy spokesman in Washington, D.C., would not say why the two wharves could not be farther apart.

In court filings, the Navy argued that deviating from safety requirements would result in "no new increased risks." The Navy said the National Environmental Policy Act protects information related to national security and that details of its analysis of explosion risks are exempt from disclosure laws.

The Navy added there is "very low probability" of such an explosion, although "thermal effects and accompanying blast wave ... will result in a loss of people and significant damage to facilities."

Glen Milner, a Ground Zero member, said the Navy's secrecy extended even to providing dimensions of the wharves. Measurements based on Google Earth, Milner said, show the two wharves are about 500 feet apart. Minimum separation under Defense Department explosives-safety standards is 2,789 feet.

The Navy has pointed out that Kings Bay, Ga. _ the East Coast base for the Trident submarine fleet _ also is operating under a safety exemption. But Milner estimates the two wharves at Kings Bay are about twice as far apart as at Kitsap Bangor.

Milner, of Lake Forest Park, Wash., said Ground Zero so far has spent $40,000 on legal fees, with much more unpaid. The group, founded in 1977, is made up of all volunteers and relies solely on donations, not membership fees.

In 2011, Milner won a ruling from the U.S. Supreme Court on a Freedom of Information Act lawsuit he filed against the Navy regarding potential dangers at its munitions depot on Indian Island, near Port Townsend, Wash.

Milner says the Navy has never seriously assessed the explosive hazards posed by the adjacent wharves and that it has quashed public debate under the guise of national security.

"We are not afraid to take on the Navy. And we have proven our case," Milner said. "The Navy wanted its wharf, and what others thought about it did not matter."

The second wharf is scheduled to be finished in 2016. The Navy estimates it would create 4,370 direct jobs and 1,970 indirect jobs.