For more than a decade, Hangar One has been stripped down to its skeletal frame, unused and exposed to the elements. At times, it wasn't clear what the future held for the iconic military structure that's visible from Highway 101, and whether it would ever be restored to its former glory.

In recent weeks, scaffolding has gone up around the massive structure at Moffett Field and long anticipated restoration work has finally begun. Between now and 2025, crews will clean Hangar One of contaminants, install new cladding onto the steel frame and repaint the airship hangar so it will look nearly identical to its old self.

The announcement marks a moment of celebration for those who have fought to preserve the landmark, including U.S. Rep. Anna Eshoo. In a statement Monday, Eshoo described Hangar One as an "American icon" with a standout structural design – a freestanding megastructure covering 8 acres in the northern end of Mountain View.

"Our community has worked for years to save this historic landmark that defines the landscape of the South Bay region and Silicon Valley," Eshoo said.

Moffett Field, including Hangar One, was built in 1933 as a West Coast base for the U.S. Navy's "lighter than air" dirigible program. Hangar One was constructed to house the U.S.S. Macon, a nearly 800-foot-long airship that crashed just two years later. The hangar was then used to house training aircrafts in the lead-up to World War II, when Moffett Field was recommissioned as a naval air station.

In the 1990s, Hangar One was transferred to NASA following the closure of the military base.

Leaving Hangar One in its current state was not an option. Starting in 2003, environmental studies showed that the hangar's building materials – from the frame and door-opening mechanism to the concrete floor – had high levels of polychlorinated biphenyls (PCBs) and lead. In 2008, the U.S. Navy decided the best course of action to prevent further contamination was to remove the siding and interior structure, cleaning what's left and coating the structure in a weather-resistant epoxy coating.

The clean-up efforts and partial dismantling of Hangar One raised questions and sparked debate over whether to preserve Hangar One and, if so, who would get stuck with the bill and the liability. By 2010, there was still some wishful thinking that the siding would be stripped and replaced simultaneously, in order to avoid what ended up happening: more than a decade of looking at its enormous skeletal remains.

After resolving a back-and-forth over which public agency is ultimately responsible for Hangar One -- it's NASA Ames -- the big breakthrough on how to pay for restoration work came in 2014 when Google agreed, through its subsidiary Planetary Ventures LLC, to lease the property for 60 years and pay the cost of restoring Hangar One.

The restoration work is labor-intensive. Crews will have to methodically clean about 1.8 million square feet of steel elements, removing the lead paint using a combination of media blasting – like sand blasting, but with copper slag or other abrasives – chemical stripping and scraping by hand.

From there, new exterior cladding that looks remarkably similar to the old materials will be installed on the steel frame, which is more than 1,100 feet long, 308 feet wide and 198 feet tall.

The first steps, which are visible today, involve erecting scaffolding and encasing Hangar One to kick off the cleaning and removal efforts. More recent environmental investigations have found that the epoxy coating previously meant to keep contaminants from further "migrating" has deteriorated in several areas, and that there are signs of rusting and levels of asbestos and lead detected on the site.

Greg Unangst, a Mountain View resident and member of the Restoration Advisory Board monitoring the efforts, said he saw the scaffolding last week and that it marks the beginning of remediation that had been worked on behind the scenes for years. He said it'll take a couple years of work before the reskinning process will begin, but that the results will bring back Hangar One as it once was.

"If (Planetary Ventures) can successfully complete their plans, the hangar should look very much like it looked in the 1930s, only better, without the asbestos, lead and PCBs," Unangst said.