One of the largest office-leasing deals of 2014 slipped quietly under the radar in the spring when the U.S. Drug Enforcement Administration renewed nearly 600,000 square feet in West Chelsea, The Real Deal has learned.

The New York division office of the federal law enforcement agency signed on with Hirschfeld Properties in May to renew its 570,000 square feet at 99 Tenth Avenue, a 10-story former industrial building occupying a full block between the High Line and the Hudson River.

The DEA, which has been in the building since 1991, will pay an aggregate rent of $341.9 million over the 15-year term according to the Government Services Administration, which manages real estate for federal agencies.

The lease is effective starting June 2016.

Hirschfeld Properties’ president Elie Hirschfeld said it took a fair bit of negotiating to keep the agency in the nearly 100-year-old building, a former cold-storage warehouse that needed windows punched through the blank brick walls when it was converted to office use in the 80s.

“It was a complicated transaction that took a couple years to finalize in order to accomplish all their objectives,” such as upgraded technology and security measures, Hirschfield said, “the details of which I’m not at liberty to speak about because of the high-security nature.”

The DEA deal ranks as the fourth-largest office lease of the year, in between Time Inc.’s roughly 730,000 square-foot lease at Brookfield Place and Sony’s deal to take about 550,000 square feet at 11 Madison Avenue, according to a yearly report compiled by CompStak.

The DEA’s New York Organized Crime Drug Enforcement Strike Force also inked a lease at Brookfield Place in March for 56,000 square feet.