When a breathless Jonas Cattell dashed into Fort Mercer that October day in 1777, the enemy wasn't far behind.

Hours earlier, the 18-year-old had overheard talk of an attack on the American fort and ran the 10 miles from Haddonfield to Red Bank, Gloucester County, bypassing Hessian mercenaries along the way.

His timely warning gave the American defenders time to reposition their artillery and set a trap that decimated the Hessians.

About 400 of them - a third of the German force - were mowed down by cannon and musket fire, then buried in a mass grave at what is now Red Bank Battlefield Park.

Next spring, that site will become an archaeological dig, funded with a $46,200 grant from the National Park Service, Gloucester County officials said.

The ground, along trenches and near a monument commemorating the battle, will be surveyed by a professional firm using ground-penetrating radar and other tools.

Artifacts including musket balls, grapeshot, swords, buttons, buckles, and other uniform accoutrements are likely to be recovered and eventually exhibited, park officials said. The human remains will be offered to the German government, or reburied in place and marked.

"This will bring a lot of attention to the site and provide an opportunity to tell the story of the Revolution in South Jersey," said Jennifer Janofsky, a Rowan University history professor and curator of the Red Bank Battlefield and Whitall House.

"We're in the shadow of Philadelphia, but there were more battles fought in New Jersey than in any other colony," said Janofsky, whose students will help sift through the soil for artifacts as part of a field trip. "It's time for people to realize the important role we played."

The Park Service funding was a coup for Gloucester County, officials said. "These grants are extremely competitive," Freeholder Director Robert Damminger said. "Each year, about 30 sites around the country receive funding, so it's truly an honor for us to be selected for the grant."

The planned dig follows improvements at the site, including a $136,000 walkway providing better access to the Whitall House, which was used as a hospital during the battle, said Chuck Rose, county director of parks and recreation.

The archaeology grant was a surprise. "We didn't think we'd get it," Rose said.

The battle was very important, said Frank DiMarco, liaison to the county Department of Parks and Land Preservation. "Most people don't know how important, but the history behind it is coming to light now."

The stakes were high on Oct. 22, 1777, as the Hessians left Haddonfield.

Fort Mercer and its Pennsylvania counterpart, Fort Mifflin, had trained artillery on the Delaware River to prevent a dozen British ships from supplying the 18,000-strong redcoat army occupying Philadelphia.

The vessels were forced to sail directly into the forts' line of fire by chevaux-de-frise - iron-tipped logs set in the river to sink or disable enemy ships.

Without the supplies, the British couldn't hold the city, much less pursue the Continental Army under George Washington, who told Mifflin's commander to hold the fort to "the last extremity."

On the New Jersey side of the river, Mercer's defenders knew Hessians were likely to attack, and they reconfigured the fort - with a French engineer's help - "to make it more defensible," Janofsky said.

Up to 400 colonists, including about 100 African Americans, manned the fort, commanded by Col. Christopher Greene. They faced at least 1,200 mercenaries.

But Cattell's warning "allowed the defenders to move their artillery pieces and alert the Navy," Janofsky said.

The Hessians under Count Emil Kurt von Donop soon passed over a wall of pointed logs and thought they'd breached the fort.

Instead, they fell into a trap and were met with a deadly hail of artillery and musket fire from behind earthen works. The attackers' numbers were further thinned by bar-shot - two cannon balls connected by an iron bar - fired from American vessels.

Von Donop was shot through the upper part of the leg and later died, Janofsky said, adding, "Once the Hessians lost their leadership and their northern flank, everything fell apart."

The British faced more bad news the next day. The 64-gun Augusta came under heavy fire, struck the shoals on the Jersey side, caught fire, and blew up.

"The explosion was so loud that it blew out windows in Philadelphia," including at the Walnut Street jail, which was across from what is now Independence Hall, Janofsky said.

In the days that followed, burial crews dug mass graves and interred the Hessians. Some American dead from Fort Mifflin were later brought across the river and are also believed to have been buried at the site, which covers about the size of half a football field.

The battles at Mercer and Mifflin proved crucial. By their own estimation, the British had lost two of the most precious months of the war, along with several large warships. Short on supplies, they eventually left Philadelphia and crossed the river to New Jersey, where they fought an inconclusive battle at Monmouth Court House.

Nearly 237 years later, unearthing the history at Mercer will be a teaching moment.

About 1,200 elementary school students will visit the site during the dig and will be allowed to touch objects, Janofsky said. "Another great thing about it is that we will take my students out of the classroom and get their hands dirty."

"They will work side by side with the archaeologists," she said. "We're thrilled."