Submarines can dock at Portsmouth Naval Shipyard without tidal help. Here's how.

KITTERY, Maine — Portsmouth Naval Shipyard leaders announced the finishing touches are complete on a $158 million super flood basin, allowing submarines to dock without buoyancy assistance, comparable to a navigational lock.

Last month, the USS Cheyenne, which arrived for scheduled maintenance and system upgrades in November, became the first submarine to dock at the shipyard’s Dry Dock 1 area using the super flood basin. Submarines in the past needed docking help from a buoyancy assist system, which utilized large, floodable, air-filled tanks during peak high tide.

The super flood basin now allows for submarines to dock and undock without relying on the Piscataqua River’s tides. Shipyard and project leaders celebrated at a ribbon-cutting ceremony Thursday.

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“The opening of the super flood basin is a major milestone for Portsmouth Naval Shipyard ensuring we have the right capabilities to successfully execute our mission in support of the submarine fleet,” said shipyard Commander Capt. Michael Oberdorf in a prepared statement. “The week of April 11 we were able to dock Cheyenne in Dry Dock No. 1 without buoyancy assist tanks, a first for our shipyard.”

The shipyard’s Dry Dock 1, where Navy attack submarines are repaired, maintained and modernized, is undergoing a federally-funded, $1.7 billion expansion. The seven-year project is part of the Navy's Shipyard Infrastructure Optimization Program.

Dry Dock 1, according to the shipyard, is the shallowest of the shipyard’s three existing docks.

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“The super flood basin project modified existing structures, parts of which were built in 1845, to allow the docking of submarines regardless of the tide,” the shipyard wrote in its announcement.

Capt. Frank Carroll, the officer in charge of the super flood basin’s construction, said the project required more than 34,500 pounds of underwater explosives to be blasted and three dive crews building the basin simultaneously. The shipyard noted that the basin “impounds” 20 million gallons of water — the equivalent of 40 Olympic-sized swimming pools — at a 16-foot differential from the river.

Aside from the Portsmouth Naval Shipyard and the Navy, Carroll commended the Naval Facilities Engineering Systems Command, Naval Sea Systems Command and two contractors, Cianbro and Stantec, for their work on the basin.

“It truly was a team effort throughout the project,” Carroll stated.

The shipyard’s Dry Dock 1 was initially constructed during World War II, with the first three submarines launched from it on Jan. 27, 1944.

A new phase of the Shipyard Infrastructure Optimization Program project will “bisect” the basin and create two additional dry docks, per the shipyard.

“It took a great deal of planning and construction work to get us where we are today, and while we still have a lot of infrastructure optimization work ahead of us, this is a huge win for the shipyard and the Navy,” Oberdorf added.

The 360-foot long USS Cheyenne is the third submarine with Cheyenne, Wyoming as its namesake and will be the first Los Angeles-class submarine to undergo a service life extension at the shipyard.

This article originally appeared on Portsmouth Herald: Submarines can dock at Portsmouth Naval Shipyard without tidal help