The three-story headhouse, measuring 175 by 26 feet (53.3 by 7.9 m), contains a central tower with a penthouse and is flanked by pavilions on its western and eastern ends.

[8][9] Major developments on the West Side were erected after the Ninth Avenue elevated line opened in 1879, providing direct access to Lower Manhattan.

[12] The building is three stories tall and is composed of two sections: a symmetrical headhouse to the north, measuring 175 by 26 feet (53.3 by 7.9 m), and a drill hall to the south, a large space spanned by steel trusses.

[4] The facade contains many castellated architectural elements, including deep openings, turrets, cornices with machicolations, and parapets with crenellations.

The upper stories contain many elements of late-19th and early-20th-century architectural revival styles, including red and gray brick in Flemish bond, as well as granite window surrounds with classical details.

[19] Although the building was patterned after old fortifications, only some design elements, such as the granite base, central tower, and recessed areaways on 66th Street, served a defensive purpose.

As of 2011[update], the headhouse's roof contains HVAC equipment, emergency generators, a boiler flue, and stair bulkheads, while an elevator shaft and cooling tower are placed atop the penthouse.

[24] The primary portions of the facade on 66th Street, between the central tower and outer pavilions, are placed behind an areaway with an iron fence and granite posts.

[23][16] The upper stories largely contained one-over-one sash windows with wood frames, inset within granite surrounds;[24] these were replaced with aluminum replicas in 2004.

The light court contains a ground-level doorway leading to the drill hall's basement, as well as a metal boiler flue on its northern wall.

Behind the setback, the eastern wall was originally divided vertically into three bays, each with three wooden sash windows, as well as an oculus with a hexagram near the top of the facade.

The southern elevation of the headhouse is made of brick and is not visible from the street, but it has skylights, aluminum windows, and metal doorways which were all added in 2011.

[30] The superstructure was intended to be fireproof and included brick walls, cast-iron columns, reinforced concrete floor slabs, and steel girders.

[35] The basement contained a horse stable with 64 stalls, a gun lift, a shooting range, a storeroom for armor and ammunition, a harness room, bathrooms, and mechanical equipment.

[14][37] The main entrance led directly into the central stair hall,[37] which contained mosaic tiles and marble wainscoting.

[33][b] During the building's 1977 renovation, the existing decorations were gutted, and ABC added carpet-tile floors, acoustic-tile ceilings, and concrete-and-gypsum-board walls.

[44] A stair leads between the third story and the penthouse, where there is a conference room with a raised concrete-tiled floor, gypsum-board ceiling, and brick walls.

ABC sealed some of the windows with CMUs, installed catwalks and acoustic panels on the ceiling, and moved the freight elevator from the northwest to the southwest corner.

[53][58] Wendel first requested that the New York state government provide funding for a dedicated armory building in 1884, but no action was taken on that proposal.

One of the National Guard appointees, First Brigade commander McCoskry Butt, had wanted the board to be selected via a competitive bidding process, but Van Wyck replied that his commissioner of buildings should have complete discretion in choosing the architect.

[95][96] The First Sanitary Train of the New York National Guard (later the First Field Ambulance Corps) moved into the First Battery Armory after the First Battalion had relocated.

[96] Over the years, the building served less of a defensive purpose; the turrets and horse stables became storage space, and terrazzo tiles depicting the 102nd's insignia were installed on the floor of the main lobby.

[104] With the onset of World War II, in 1940, the New York state government stopped renting out the armory for civilian events,[105] and the 102nd Medical Regiment was mustered into service.

[86] After World War II, the 102nd Medical Armory hosted events such as Open Exhibition of Colorful Tropical Birds and Canary Types[107] and motor-vehicle inspections.

[86] The tennis court was managed by the Lincoln Plaza Racquet Club, whose operator Jason H. Smith Jr. paid $1,000 per month in rent.

[117] The project also involved removing almost all the old finishes, relocating partitions, painting the side elevations of the facade, and modifying the front entrance.

[86][41] The city government's Industrial and Commercial Incentives Board approved a tax abatement for the armory's renovation in April 1977.

[117][116] ABC announced in 1986 that it would relocate most of its New York City offices from Midtown Manhattan to Lincoln Square, creating a headquarters "campus" around 66th, 67th, and 68th Streets.

[121] By the 1990s, fans of One Life to Live frequently congregated around the armory during tapings, hoping to meet the show's cast members.

[125] Disney sold most of its Upper West Side campus in 2018 to Silverstein Properties but retained ownership of the First Battery Armory.