On this day 23 years ago, the worst terrorist attack on American soil unfolded. Two highjacked planes crashed into the World Trade Center in New York, One hijacked plane crashed into the Pentagon in Washington, D.C., and the fourth United Airlines Flight 93 crashed into a field in Somerset County Pennsylvania.

The field is now the site of Flight 93 National Memorial. At 9:28 a.m. on September 11, 2001, Flight 93 was heading from Newark, New Jersey to San Francisco. Four men in firs stormed the cockpit and hijacked the plane.

“What happens afterwards, of course, we only know of because of the phone calls that are made aboard Flight 93. And in the next 20 minutes, 13 people aboard Flight 93 are going to make a total of 37 phone calls. And that's going to tell us what was going on aboard the plane. But more importantly, it's going to tell what was going on the ground to the crew and passengers, “said Katie Hostetler, Public Information Officer for the National Park Service.

A lot of the calls were made from an airphone that was in the back of the airplane where the crew had been pushed. Only two calls were made from cell phones. As the members on the plane made phone calls to their loved ones, they learned what happened at the twin towers and the pentagon.

“And then we know that they've taken a vote for Flight 93 because they mentioned that in their phone calls to their loved one. And they decided that they're going to try to get into the cockpit door. There's about six folks. And in a similar way, we're getting ready to do it. It's happening. Everyone's running to first class. And there's two phone calls that are not hung up. They leave the phone on the seat intending to come back to their loved ones and let them know what they've accomplished aboard that airplane.”

The passengers made a heroic attempt to reclaim the plane. During the struggle, the plane lost control and crashed into a field near Shanksville, Pa. Everyone on board were killed, however through the passenger’s bravery, the prevented the hijackers from reaching their target.

“The people aboard Flight 93 were just regular people. They were going to visit friends or go to a birthday party or travel and see national parks. And they're all traveling for very different reasons. And they find themselves in this extraordinary circumstance. And they didn't have to do anything. But through the phone calls that they make, they learn about what's going on. And they chose to do something. And that's the power I kind of really hope the next generation takes with us. And then also that, you know, just telling someone this story makes a difference, too. If you tell one person about what this incredible story does and means to a lot of other people, it continues that word-of-mouth association as well.”