The British army was not an idle observer of these movements. On the twenty-second of October, the two Grenadier regiments of Donop and Minnigerode, and two regiments of the line, with the Infantry Chasseurs (all Hessian), with eight 3–pounders and two howitzers, approached Fort Mercer and demanded its surrender. They had crossed at Coopers Ferry on the twenty-first, slightly interrupted by skirmishers, and on the following morning suddenly emerged from the woods, expecting an easy and an immediate victory. Defiance was returned to their demand. Two assaulting columns, already formed, made an immediate and simultaneous advance upon the north and south faces of the fort. The garrison, however, knowing that it could not hold the exterior works, which were still incomplete, retired to the interior defences; but still occupied a curtain of the old works, which afforded an enfilading fire upon any storming party which should attempt the inner stockade. The withdrawal of the garrison from the exterior works was misunderstood. The assault was bold, desperate, and brilliant. The resistance was incessant, deadly, overwhelming. Colonel Donop fell, mortally wounded, and near him, Lieutenant-Colonel Minnigerode. These confident assailants lost, in less than sixty minutes, four hundred men—being one-third of their entire force. And still, one more attempt was made at the escarpment near the river; but here also the Americans were on the alert. Armed galleys in the stream opened a raking fire at short range, and dispersed the assailants. Two British ships—the _Augusta_ (64–gun man-of-war), and the _Merlin_ (frigate), which had been so disposed as to aid the assault, grounded. On the next day, the former took fire from a hot shot, and blew up, before her entire crew could escape; and the _Merlin_ was burned, to avoid capture. The American loss was fourteen killed and twenty-one wounded. Colonel Donop was buried carefully by Major Fleury, a French officer in the American service, and his grave at the south end of the old works is still an object of interest to visitors. Colonel Greene, Lieutenant-Colonel Smith, and Commodore Hazlewood of the galley service, received from Washington and from Congress worthy testimonials for “gallant conduct.” In the meantime, the British had found two solid points of land amid the marshy ground at the mouth of the Schuylkill River, within cannon-range of Fort Mifflin, where they constructed two heavy batteries bearing upon that fort. Four 32–pounders from the _Somerset_ and six 24–pounders from the _Eagle_, with one 13–inch mortar, were added to works erected on Province Island, to bring a more direct fire upon the fort than could be secured from the batteries at the mouth of the Schuylkill River. (See map.)