In 1865 Francis Bannerman VI opened a military surplus store near the Brooklyn Navy Yard in New York, buying up old Civil War equipment from the government at a wholesale price and offering them to the general public. The business proved to be lucrative, and the family soon opened a second store on Atlantic Avenue selling worn out rope that could be made into paper products. A third store opened on Broadway in 1897 to outfit soldiers volunteering for the Spanish-American War, which brought on even more business; Bannerman had managed to purchase over 90 percent of the Spanish weapons and ammunition captured by the United States. The Bannerman's voluminous 300-page catalog remains an excellent reference for collectors of antique military equipment.
Bannerman's storeroom in New York City was too small and too dangerous to hold the thirty million surplus munitions cartridges he had managed to accumulate, so he purchased an entire island in the Hudson River for this function. Pollepel Island (Dutch for "wooden ladle") is a 6.5 acre rocky outcrop, located about 50 miles north of the city. The island has been largely uninhabited through known history; Native Americans believed it to be haunted, and early Dutch sailors feared resident goblins who could allegedly whip up squalls that could sink a vessel (a horseshoe nailed to the mast was said to be an excellent deterrent). Drunken sailors would also be left on Pollopel to sober up. When Bannerman bought the island in 1900, it had only been used for occasional summer picnics.
Construction of the massive arsenal on Pollopel Island began in 1901. Bannerman himself designed the buildings, often decorated with military items from his collection, and let the constructors interpret his designs as they saw fit. Using his Scottish heritage as inspiration, he envisioned three warehouses, a family residence, worker's houses, and a massive six-story tower, all with crenelated towers, turrets, and there was even a working drawbridge (although "Moat Brae" was never completed). The massive brick facade of the tower provided an excellent advertising space to promote his business to anyone traveling up the Hudson via ship or rail. In the early years, visitors would gather on a spot on the eastern shore of the river and ring a brass bell, signaling the employees to bring their rowboats across. It was common to bring jugs of drinking water onto the island, since the river water was not potable. Construction was halted when Bannerman died in 1918, but the business continued to operate under his sons, Frank VII and David.
Although the facility was much more secure and safer than storage in the heart of Manhattan, accidents still occurred. In 1920, 200 tons of munitions exploded, injuring three people and catapulting a 25-foot long chunk of stone onto the shore of the mainland, damaging the rail line that ran along the river. Another time, a cannon mistakenly fired a shell over a nearby mountain and through a barn (although no people or animals were injured). Lighting strikes were also common, due to its position on the open water and the number of flag poles located on the buildings.
A ferryboat named Pollepel supplied transport to the island in later years, replacing the employee-driven rowboats, but in 1950 a major storm sent her to the bottom of the Hudson River. In 1959, the family decided to move the Manhattan business to Long Island and empty the store on Broadway and Pollepel Island's castle of all remaining supplies. The NYPD bomb squad and U.S. Army detonated or sunk most of the inventory in New York Harbor. The island was sold to New York State's Taconic Park Commission in 1967, and on August 9th 1969, a suspicious fire destroyed the wooden floors and roofs of the buildings and left the entire island in ruin. The island remained off-limits due to submerged bulkheads, collapsing brick facades, and unexploded ordinance possibly buried in the rubble, however many curious visitors have strolled through the ruins over the years.
On December 28th 2009, an official on the Metro-North rail line noticed an entire corner of the massive tower collapsed due to the weathering of the aging mortar and unprotected bricks. Officials estimated 30-40 percent of the front wall and about half of the east wall was gone.
In recent years, the Bannerman Castle Trust was founded to preserve the island. Along with building docks and repairing some particularly dangerous areas, they also hold walking tours and various events under their supervision.
Brian Altonen has a wonderful page with photos of the island taken around 1960, showing some of the vintage weapons that were stored there being hauled away by boat and more history about Bannerman's business.
