KITTERY, Maine (AP) The Navy’s improvements at Portsmouth Naval Shipyard are taking a big step forward.

Maine-based Cianbro spent a year-and-a-half building the 5,000-ton, precast concrete entrance for one of the shipyard’s three dry docks. It arrived by barge on Monday.

The so-called “Superflood Basin” project will make the shipyard less reliant on tides and allow Virginia-class attack submarines to enter Dry Dock No. 1 without a buoyancy assist system.

It’s part of the Navy’s long-term upgrades to four public repair yards to speed maintenance and return ships and submarines to the fleet faster at a time of growing threats.