The Brooklyn Navy Yard is nearly half the size of Prospect Park, but was, until very recently, one of the least accessible areas to the general public in the borough.

But with the opening of Building 77, which debuts today, the public will be welcomed for the first time into one of the complex’s most formidable buildings: a hulking 1 million-square-foot block of concrete that’s considered the heart of the entire Brooklyn Navy Yard redevelopment.

The companies leasing space in Building 77 are poised to bring in 3,000 new jobs, setting the complex well on its path of creating 17,000 jobs by 2020. David Ehrenberg, president and CEO of the Brooklyn Navy Yard Redevelopment Corporation, the nonprofit overseeing the yard’s rehabilitation, says the goal is to create the largest job expansion the Navy Yard has seen since World War II, when some 70,000 people—or .02 percent of the American workforce—labored within its confines.

In its heyday, Building 77 served as a Navy storage warehouse and offices for the naval high command for the North Atlantic fleet and the commandant of the yard. A major part of the building’s $185 million rehab consisted of removing 3 million pounds of concrete from the building and installing 50,000 square feet of windows. It’s that act, Ehrenberg says, that transformed the building from a warehouse to an active manufacturing facility.

Most of the jobs at Building 77 will be in light manufacturing, with food purveyors and retail space housed on the ground floor. Here, anchor tenant Russ & Daughters will churn out the bialys, bagels, and other delicacies that the 103-year-old appetizing institution is known for. The company will have a small retail space, along with a larger hub where goods will be made for the business’s Manhattan satellites and nationwide shipping program.

Niki Russ Federman, a third-generation operator of Russ & Daughters, says the Navy Yard encouraged the company to use the bulk of its 14,000 square feet for manufacturing space. “That was music to our ears—that's not what you hear from most landlords,” Russ Federman says. “As a business, once you get to a certain size, it’s very hard to stay and operate in the city. At the Navy Yard, we saw a base where we could grow and stay for decades.”

Joining Russ & Daughters are Brooklyn-based salsa company Jalapa Jar, Rustik Tavern, and Transmitter Brewery, among others. Each food purveyor will have a small retail component, but Ehrenberg stresses that the ground floor of Building 77 is no food hall. Instead it's a place where people come to work, achieving the Navy Yard’s goal of creating high-quality, middle-class, accessible Brooklyn-based jobs.

On the building’s upper floors, rentable spaces range from about 2,000 square feet to up to 15,000 square feet; tenants already in place include metal fabrication firm Situ Studio, jeweler Catbird, and furniture maker Armada NYC. The building’s top floors will house office-based tenants, such as fashion brand Lafayette 148, which is moving its New York production operations into the building from its previous Soho location.

“It was extraordinarily important to get this building right in all of its different ways,” says Ehrenberg. “We tried not to make the building a nostalgic thing, and more an embrace of what goes on behind the scenes in New York.” Ducting isn't hidden, and spaces are finished only so much as they need to be to function for their occupants. “We want people to see that manufacturing still happens in Brooklyn,” Ehrenberg continues.

As of its opening day, the building is 85 percent occupied, signaling the city’s need for long-term manufacturing space. The nonprofit running the Brooklyn Navy Yard hopes to see that demand for local space, and New York-based employees, grow. The nonprofit not only works to supply the space to tenants, but also provides skill enrichment and training courses in Building 77 that it hopes will help bring jobs to the existing community.

The nonprofit is partnering with the Department of Education, specifically eight nearby high schools, to provide different courses of vocational training for students that will ensure they graduate with the most current and prescient skills in manufacturing.

“Technology is moving really quickly,” Ehrenberg says, noting that the curriculum, informed by the building’s tenants, will help graduating students stay competitive in the job market. The nonprofit’s community outreach also extends to groups that are traditionally disenfranchised in the job market, like ex-offenders.

The opening of Building 77 will give the nonprofit the opportunity to turn its focus to the 120,000 square feet of office space that will top the Navy Yard’s vaunted incoming Wegman’s, which will replace the now-demolished mansions of Admiral’s Row.

Ehrenberg jokes that it's his successor’s successor’s successor who will get to see the Navy Yard achieve the full scope of its potential, though it doesn't seem to bother him.