BOSTON (AP) – A civilian employee of the U.S. Navy fell about 70 feet and died while preparing the historic USS Constitution for its July 4 Boston Harbor turnaround.

John C. Monaghan Jr., 56, of Windham, N.H., fell from a platform on the ship’s main mast to its top deck around 12:10 p.m. on Wednesday, the Navy said in a statement.

Monaghan worked in the ship’s maintenance and repair facility for the Naval Historical Center in Boston. He was performing routine maintenance on the Constitution’s mast and rigging for the holiday weekend. The Constitution is annually taken out into Boston Harbor and returned to its berth facing the opposite direction.

Between 80 and 100 visitors were touring the ship at the time of the fall, the Navy said.

Two unidentified people performed CPR on Monaghan, who was taken to Massachusetts General Hospital, where he was pronounced dead on arrival.

His son, Ross Monaghan, 26, told The Boston Globe that his father left an engineering job to work on square-rigged ships, and loved his new vocation.

Petty Officer Matt Chabe said Monaghan was wearing proper safety equipment, including a harness and a hard hat.

The Constitution, known as “Old Ironsides,” is the oldest commissioned ship afloat in the world, but is used mainly as a museum.

Tours were suspended after Monaghan’s fall, but they resumed on Thursday.

The crew of the Constitution will observe a moment of silence for Monaghan during Sunday’s tour of Boston harbor.

Several agencies are investigating the cause of the accident.

AP-ES-07-01-04 1520EDT