Bannerman’s Island Arsenal on the Hudson

Riding the Hudson Line of New York’s Metro North Railroad is always a treat. The tracks, first laid out in the 1840s, run alongside the banks of the Hudson River, weaving together a chain of small towns whose very names evoke visions of the good life: summer weekends spent away from the bustle of Manhattan, peeping the blaze of autumn foliage in the Hudson Highlands, or strolling the main streets of Tarrytown or Cold Spring, shopping for antiques or top-quality pastries. New York’s Hudson Valley is a marvelous open secret, and the Hudson Line makes it accessible to all.

Of the many splendid views riders pass along their journey up or down the river, including landmarks such as the New Jersey Palisades, the Bear Mountain Bridge, and the citadel of West Point’s Military Academy, there is nothing quite like the shock of spotting Bannerman Island. Situated between Cold Spring and Beacon, the island sails by in a flash, but for more than a century, keen-eyed passengers have been treated to a glimpse of what appears to be the ruins of a long-forgotten fairy tale: Bannerman Castle. Piled like some red-brick wedding cake, the castle’s many towers, turrets, and crenellated gateways are a remnant of a bygone era, built by a Scottish-born entrepreneur named Francis Bannerman.

Francis Bannerman VI was born in Dundee, Scotland in 1851. At age three, he emigrated to New York with his parents, Francis Bannerman V and his wife Margaret, ultimately settling in Brooklyn. The elder Francis supported his family by working as a purveyor of maritime supplies, otherwise known as a ship chandler. By the end of the American Civil War in 1865, the younger Francis, now a teenager, was contributing to the family’s stability by buying and reselling surplus military equipment, building his enterprise into a surprisingly successful business.¹

The elder Francis opened a shop at 14 Atlantic Avenue sometime between 1869 and 1870, just a stone’s throw from the Brooklyn waterfront near the modern-day Pier 6 ferry stop.² Two years later, he died, leaving his son to forge his own path at the age of twenty-one. Listed under the deceptive label of “hardware merchant” or “metals trader,” what Bannerman was actually doing during the waning decades of the nineteenth century was amassing one of the nation’s largest collections of government weaponry, munitions, uniforms, and other goods, often bought as less-than-wholesale prices in the aftermath of foreign wars.

An 1892 advertisement for Bannerman’s business in The Sun’s Guide to New York proclaimed his operation at 27 Front Street in Manhattan, just north of Broad Street. “Dealers in Cannons, Projectiles, Carbines, Rifles, Swords, Military Equipments, Flags, Tents, Saddles, Spears, Revolvers, Pistols, War Relics, Trophies, Autographs, Military Curiosities, etc.” The ad continues, “Our Salesroom is pronounced one of the finest Military Museums in the country, and is one of the sights of the city. Visitors are welcome.”³

A natural showman and marketing savant, Bannerman continued to blur the line between retail shop and history museum. His collection of munitions expanded drastically as he bought up surplus stock from both the Spanish and American governments following the end of the Spanish-American War in December 1898. Photos from this era depict Bannerman, smartly dressed, bespectacled, and bearded, sitting at his desk quite literally surrounded by piles of guns and shells.

Bannerman struggled to store his volatile collections, which were sprawled across properties in Manhattan and Brooklyn. They posed formidable risks to life and property, sited as they were in the middle of some of the densest districts of one of the largest cities in the world. In 1902, he was sued after a fourteen-year-old boy was injured when a lump of brass-speckled gunpowder exploded in an empty lot owned by Bannerman in Brooklyn.⁴

Out of space and in danger of further legal woes, Bannerman’s unusual predicament required an equally unusual solution. In 1901, he purchased Pollepel Island, a rocky spit of land in the middle of the Hudson fifty miles north of Manhattan and transformed it into his headquarters and retreat. On the island, he built a harbor, wharves, employee housing, and a cozy hilltop home for his family. But what dominated the island’s profile was the six-story arsenal: designed entirely by Bannerman and completed in 1908, it was built to resemble a Scottish castle made of brick and concrete. Emblazoned across its northern facade were the words BANNERMAN’S ISLAND ARSENAL.

Visible from trains running south of Beacon, the arsenal became an instant landmark on the Hudson. Into it, Bannerman moved his vast collection of Spanish-American War relics along with cannons, carriages, swords, uniforms, and all types of munitions and explosives. It was all quite a spectacle for such a remote and bucolic location, with red flags, spotlights, and guard dogs warning troublemakers away. But all this defense only increased widespread interest in Bannerman’s business, which flourished as the outfitter of choice for collectors, reenactors, and even revolutionary militias. “The countries along the equator knew Bannerman as a dependable source of supply when presidents were to be ousted,” wrote The Sun following his death in 1918. “He furnished war’s goods for the good gold of peace” and was highly successful in his endeavors.⁵

In Manhattan, Bannerman’s business had moved uptown. In 1905, he purchased a five-story cast-iron loft building at 501 Broadway, one of that thoroughfare’s busiest stretches between Spring and Broome Streets in what is now Soho.⁶ The building’s lower floors functioned as a shop and showroom while its upper floors were set up as a military museum. Newspaper advertisements proclaimed his to be the “Largest stock in the world Government Auction Goods” with a purported fifteen acres of storage space.⁷ But upriver, his fairytale arsenal became a favored retreat for the Bannermans, who spent many years enjoying the island oasis he created there.

Beyond Bannerman’s business success, his generosity made headlines several times during World War I: in 1914, he gifted 1,000 uniforms and rifles to the Lord Mayor of London to help with the war effort; in 1918, he gifted a number of cannons to the United States military as well as tens of thousands of garments to Belgium as part of the postwar relief efforts there. The total value of all his contributions amounted to more than $100,000. But he also stirred up legal troubles, most notably in early 1918 when he was accused of profiteering for trying to sell to the United States Government a lot of thirty cannons for $450,000 which he had purchased at auction just six years prior for $78 each.⁸

Francis Bannerman VI died on 26 November 1918 at Brooklyn’s Hotel Margaret, which once stood at 97 Columbia Heights. The New York Times cited overwork from his wartime benevolence as the reason for his untimely demise.⁹ He left behind a wife, Nellie, and three sons, Frank, David, and Walter, who oversaw the family business in his absence.

In 1920, an ancillary building on the island exploded, sending a slab of brick wall sailing across the river. “A barrage of shot and bullets from the stores of ammunition which were exploded, accompanied by a dense cloud of smoke, prevented boats which set out from the shore from reaching the island for some time,” The New York Times reported.¹⁰ Bannerman’s widow, along with her sister, Mary Dubois, and the island’s superintendent, Charles Kovash, were on the island at the time, but none was seriously injured.

Following the explosion, the island was visited less and less by the Bannermans. They stopped using it almost entirely by the late 1940s, and its fanciful buildings fell into disrepair, though it continued to house untold thousands of weapons and explosives. Watchmen were retained to ensure no unwelcome visitors stormed the island’s beaches. While some reportedly tried over the years, “none maintained a beachhead for long,” reported David Bannerman in a 1956 New York Times interview. “They always get off,” he continued. “They know we’re ready for ‘em.”¹¹

The castle became an increasingly mysterious landmark on the river, passed daily by tens of thousands of commuters riding the New York Central System’s Hudson Line to and from Grand Central Terminal. The Bannermans finally sold the property to New York State in 1967, which intended to fold the island into the newly-created Hudson Highlands State Parks.¹² But the advance decay of the island’s structure made it unfit for visitors.

Worse still, Bannerman’s colossal arsenal burned spectacularly in 1969, leaving only its brick exterior standing.¹³ Though it was designed to look like an impregnable fortress, it had been built more like a regular warehouse, with simple wood and iron framing behind its brick curtain walls. With every scrap of wood consumed by the conflagration, its walls were left freestanding, doomed to collapse over time. Nature reclaimed Bannerman Island for the next quarter-century, with poison ivy bearding its facade and flocks of geese establishing a nesting colony along the stone terraces of the Bannerman family’s once-proud gardens.

Salvation for the island arrived in 1993 with the creation of the Bannerman Castle Trust, a non-profit organization formed to oversee the stabilization and restoration of its various structures. For three decades now, an army of local volunteers have cleared the island’s overgrown paths, uncovered and replanted acres of plots, and even constructed a new dock and restroom facilities to allow for a new flow of visitors. More extraordinarily, the Bannerman home has undergone a loving and tedious restoration, its Gaudi-esque turrets and castellations recreated, one piece at a time, by a team of artisans.

Today, guided tours are available regularly, whisking guests to the island by small watercraft almost daily. The island hosts theatrical performances in its small wooden amphitheater, and occasional dinner parties serve as fundraisers for continued restoration work. Unfortunately, despite all best efforts, the arsenal itself remains a ruin, its compromised walls collapsing with fearsome regularity. Enormous metal braces were added in 2017, but even so, a chunk of one wall tumbled to the ground in early 2025. It is unclear how much longer the remaining shell can remain standing.

The island and its castle are fanciful, beloved pieces of New York history. The life of Francis Bannerman, the immigrant millionaire who cobbled his fortune from the discarded detritus of a war-torn era, is the sort of self-made success that makes New York a perennial destination for big thinkers, dreamers, and doers from around the world. Anyone with a passing interest in his story, or that of his castle, ought to arrange passage to his island without delay; there is no telling how much longer it might last. Whatever the future holds for this unusual place, the Bannerman story will endure.

The Bannerman Castle Trust is regularly looking for volunteers to work on the island’s continued rehabilitation, events, and gardening. To learn more, visit their website.