The nation’s biggest office-to-residential conversion is hitting the market with 1,300 apartments carved from a million-square-foot brick fortress originally built to house computers — and not much else.

The former 1960s office tower at 25 Water Street, once home to JPMorgan Chase and the New York Daily News, is now a luxury apartment building with 1,320 homes and 100,000 square feet of amenities,

A hulking office tower that once hummed with the sounds of check processors and the shuffling of financial paperwork is now Manhattan’s latest high-end residential address. After a two-year gut renovation,