Cannon stolen from historic fort along the Delaware River in Philadelphia

PHILADELPHIA (WPVI) -- A cannon was stolen from historic Fort Mifflin sometime in early June, and now Philadelphia police are investigating.

The 300-pound replica signal cannon was taken from its spot on the wall surrounding the fort in South Philadelphia.

"We're a small nonprofit and this is sort of a sentimental cannon for us," said Beth Beatty, the executive director of Fort Mifflin.

The working replica was about four feet long and sat on a box on top of a 14-foot-tall wall. So stealing it was no easy feat.

"It had to be removed from this box and then removed down from the top of the wall," said Beatty. "Then it would have to be moved across the parade ground and loaded into a truck."

All that happened in early June. Officials don't have an exact date because the cannon doesn't sit in a visible area, and the first person to notice it missing thought it was taken down for maintenance.

Philadelphia police confirmed they are now involved in the search for the cannon valued at around $3,000.

"I'm sure they think this is probably their most unique assignment to date," said Beatty.

Officials at Fort Mifflin searched the entire property and even checked Facebook Marketplace to see if it was for sale. They don't believe the piece is worth much as scrap because it's made out of cast iron.

But it does mean a lot to the nonprofit.

"I would suspect this was taken by someone who finds it an appealing curiosity. And maybe it's in somebody's yard, in somebody's living room," said Beatty.

The cannon does work and it is potentially dangerous. Surveillance video didn't capture the theft.