The 1916 German attack on a New York munitions store

Though land reclamation projects have since incorporated it into the mainland, Black Tom was once a small island in New York Harbour next to Liberty Island.

In 1916 it was the most important assembly and US shipping centre for munitions and gunpowder being sent to the Allies, according to an article by Elizabeth Nix.

She says:

While the United States had not yet entered World War I and was officially neutral, American munitions dealers could legally sell to any of the warring nations. Most of the arms, however, were going to the Allies - Britain, France and Russia - because the British navy had blockaded Germany.

Wikipedia takes up the story:

After midnight on July 30, a series of small fires were discovered on the pier. Some guards fled, fearing an explosion. Others attempted to fight the fires and eventually called the Jersey City Fire Department. 

At 2:08 am, the first and largest of the explosions took place. Fragments from the explosion travelled long distances, some lodging in the Statue of Liberty and some in the clock tower of The Jersey Journal building in Journal Square, over a mile away, stopping the clock at 2:12 am. 

The explosion was the equivalent of an earthquake measuring between 5.0 and 5.5 on the Richter scale and was felt as far away as Philadelphia. Windows were broken as far as 25 miles (40 km) away, including thousands in lower Manhattan. Some window panes in Times Square were shattered. The stained glass windows in St. Patrick's Church were destroyed/

The explosion was originally put down to safety violations by workers on Black Tom. Elizabeth Nix explains:

It would take years for a persistent team of American lawyers to find sufficient evidence that showed that in fact the disaster had been plotted by the Germans. The lawyers sued Germany in the Mixed Claims Commission at The Hague, and in 1939 won the case. Germany, under the rule of Hitler, failed to pay up and the settlement was renegotiated in the early 1950s. The last payment was made to Black Tom claimants in 1979.

You can learn more about the Black Tom explosion in the video above.

One of its results persists to this day. The blast damaged the Statue of Liberty and the viewing gallery on its torch was closed. It has never reopened.