As a result of the Revolutionary War, the British Army took so many prisoners that they quickly ran out of space to hold them all. Prisons in New York, like Bridewell, were full, so the British took to using sugar houses and pro-rebel churches in the city.
In the harbor, decommissioned war ships were put to use as prison ships, the most well-known being HMS Jersey. The Jersey had – and earned – the nickname "Hell." Conditions below decks (where the prisoners were kept) were crowded – a thousand men crammed together without light, sanitation, or proper ventilation.
About a dozen prisoners died every day – from smallpox, yellow fever, malnutrition, and torture by the guards. The British sentiment was that the rebels were traitors and didn't deserve any better.
In 1782, the Assassin Connor infiltrated HMS Jersey, where he overheard a conversation between the captain and Charles Lee's mercenaries, who were trying to acquire soldiers for their master. Connor assassinated the captain without anyone noticing and then escaped from the prison ship.
At least 11,000 people died on board prison ships – more than the rest of the war put together. After the British left New York, the United States Navy found mass graves in the mud at the edge of the harbor. Those remains have since been placed under a monument in Brooklyn, where Fort Putnam used to be.