Almost two years into its four-year midlife upgrade, Nimitz-class carrier USS Abraham Lincoln (CVN-72) left dry dock at Newport News Shipbuilding in Newport News, Va. to begin the next steps of its almost $4 billion overhaul, the Navy and Huntington Ingalls Industries annouced this week.

The refueling and complex overhaul (RCOH) is the most significant maintenance period in a nuclear carrier’s lifespan. In addition to refueling the ship, the ship is almost completely refurbished and outfitted with new systems and equipment.

“Flood dry-dock and undock are called key events, but from the perspective of the crew, it is very significant in what it represents,” said Capt. Ronald Ravelo, Lincoln commanding officer in a Navy statement.

“It’s the moment we go from looking more like a building back to being a United States ship.”

Now work will focus on installing systems in the so called “rebuilding phase,” of the RCOH.

“During this process spaces will be painted, furniture will be installed, and compartment will receive finishing touches as the crew continues preparations to make Lincoln a warship that will be redelivered to the fleet,” read the release from the Navy.

Beyond Newport News, RCOH’s have become a political football in the funding debate in the era of sequestration. The Navy publicly declared in 2013 the service would have to delay the refueling of Lincoln if the service was saddled with the mandatory sequestration cuts and a continuing resolution.

As part of this year’s Fiscal Year 2015 (FY 2015) budget roll out earlier this year, the Pentagon said continued sequestration spending limits would force the Navy to forgo the RCOH for next-in-line USS George Washington (CVN-73) and decommission the carrier.

In July, Sean Stackley, Assistant Secretary of the Navy for Research, Development & Acquisition (RDA), said the Navy was talking steps to move ahead with George Washington’s RCOH.