The USS Arizona Memorial at Pearl Harbor will remain closed indefinitely because of structural issues.

The World War II Valor in the Pacific National Monument announced on Facebook that the memorial would be closed “due to a critical structural and safety issue impacting the USS Arizona Memorial dock and visitor loading ramp.”

Boat transportation to the monument was halted on May 6 after a crack was spotted developing in one of the monument’s outside walls. Maintenance crews made short-term repairs to the crack, but it quickly reappeared. The monument closed indefinitely just before Memorial Day.

In the meantime, visitors can board a free narrated boat tour of Pearl Harbor that passes nearby the sunken ship. The National Park Service (NPS) will release 1,300 free tickets for the tour every morning at 7 a.m. Visitors with tickets will also view a 23-minute documentary film before boarding the harbor tour.

USS Arizona Memorial Pearl Harbor Hawaii
Credit: Getty Images

During the closure, engineers will develop solutions to damage that was “more significant than originally anticipated,” according to Hawaii News Now.

The NPS has no estimated timeline for reopening. As soon as a timeline is available, the NPS will update the national monument’s website.

An estimated 1.8 million visitors board the USS Arizona Memorial every year. The memorial was built in 1962 over the ship’s wreckage, which was deemed unsalvageable by the U.S. Navy.

Other sites at the Pearl Harbor Visitor Center, including free museums, exhibits on the shore and the bookstore are not affected by the closure. Partner sites, including the Battleship Missouri Memorial, USS Bowfin Submarine Museum & Park, and the Pacific Aviation Museum Pearl Harbor remain open and unaffected.