The landing of troops at Tarrytown was a mere feint on the part of Sir Henry to distract the attention of the Americans; after marching a few miles into the country, they returned and re-embarked; the armament continued across the Tappan Sea and Haverstraw Bay to Verplanck's Point, where, on the 5th, Sir Henry landed with three thousand men, about eight miles below Peekskill. Putnam drew back to the hills in the rear of the village to prepare for the expected attack, and sent off to Governor Clinton for all the troops he could spare. So far the manoeuvres of Sir Henry Clinton had been successful. It was his plan to threaten an attack on Peekskill and Fort Independence, and, when he had drawn the attention of the American commanders to that quarter, to land troops on the western shore of the Hudson, below the Dunderberg (Thunder Hill), make a rapid march through the defiles behind that mountain to the rear of Forts Montgomery and Clinton, come down on them by surprise and carry them by a coup de main.
Accordingly at an early hour of the following morning taking advantage of a thick fog, he crossed with two thousand men to Stony Point on the west shore of the river, leaving about a thousand men, chiefly royalists, at Verplanck's Point to keep up a threatening aspect towards Peekskill. Three frigates, also, were to stand up what is called the Devil's Horse Race into Peekskill Bay, and station themselves within cannon shot of Fort Independence. Having accomplished his landing, Sir Henry, conducted by a tory guide, set out on a forced and circuitous march of several miles by rugged defiles, round the western base of the Dunderberg. At the entrance of the pass he left a small force to guard it and keep up his communication with the ships. By eight o'clock in the morning he had effected his march round the Dunderberg, and halted on the northern side in a ravine, between it and a conical mount called Bear Hill. The possibility of an enemy's approach by this pass had been noticed by Washington in reconnoitring the Highlands, and he had mentioned it in his instructions to Generals Greene and Knox, when they were sent to make their military survey, but they considered it impracticable from the extreme difficulty of the mountain passes.
In this ravine Sir Henry divided his forces. One division, nine hundred strong, led by Lieutenant-colonel Campbell, was to make a circuit through the forest round the western side of Bear Hill, so as to gain the rear of Fort Montgomery. After Sir Henry had allowed sufficient time for them to make the circuit, he was to proceed with the other division down the ravine, towards the river, turn to the left along a narrow strip of land between the Hudson and a small lake called Sinipink Pond, which lay at the foot of Bear Hill, and advance upon Fort Clinton. Both forts were to be attacked at the same time.
The detachment under Campbell set off in high spirits; it was composed partly of royalists, led by Colonel Beverly Robinson of New York, partly of Emerick's chasseurs, and partly of grenadiers, under Lord Rawdon. With him went Count Gabrouski, a Polish nobleman, aide-de-camp to Sir Henry Clinton. Everything thus far had been conducted with celerity and apparent secrecy, and complete surprise of both forts was anticipated. Sir Henry had indeed outwitted one of the guardians of the Highlands, but the other was aware of his designs. Governor Clinton, on receiving intelligence of ships of war coming up the Hudson, had sent scouts beyond the Dunderberg to watch their movements. Early on the present morning, word had been brought him that forty boats were landing a large force at Stony Point. He now, in his turn, apprehended an attack, and sent to Putnam for reinforcements, preparing, in the meantime, to make such defence as his scanty means afforded.
A lieutenant was sent out with thirty men from Fort Clinton, to proceed along the river-road and reconnoitre. He fell in with the advance guard of Sir Henry Clinton's division, and retreated skirmishing to the fort. A larger detachment was sent out to check the approach of the enemy on this side; while sixty men, afterwards increased to a hundred, took post with a brass field-piece in the Bear Hill defile, a narrow and rugged pass, bordered by shagged forests. As Campbell and his division came pressing forward, they were checked by the discharge of fire-arms and of the brass field-piece, which swept the steep defile. The British troops then filed off on each side into the woods, to surround the Americans. The latter, finding it impossible to extricate their field-piece in the rugged pass, spiked it, and retreated into the fort.
Sir Henry Clinton had met with equally obstinate opposition in his approach to Fort Clinton; the narrow strip of land between Lake Sinipink and the Hudson, along which he advanced, being fortified by an abatis. By four o'clock the Americans were driven within their works, and both forts were assailed. The defence was desperate; for Governor Clinton was a hard fighter, and he was still in hopes of reinforcements from Putnam; not knowing that the messenger he sent to him had turned traitor, and deserted to the enemy.
About five o'clock, he was summoned to surrender in five minutes, to prevent the effusion of blood: the reply was a refusal. About ten minutes afterwards, there was a general attack upon both forts. It was resisted with obstinate spirit. The action continued until dusk. The ships under Commodore Hotham approached near enough to open an irregular fire upon the forts, and upon the vessels anchored above the chevaux-de-frise. The latter returned the fire, and the flash and roar of their cannonry in the gathering darkness and among the echoes of the mountains increased the terrors of the strife. The works, however, were too extensive to be manned by the scanty garrisons; they were entered by different places and carried at the point of the bayonet; the Americans fought desperately from one redoubt to another—some were slain, some taken prisoners, and some escaped under cover of the night to the river or the mountains. "The garrison," writes Clinton, significantly, "had to fight their way out as many as could, as we determined not to surrender."
His brother James was saved from a deadly thrust of a bayonet by a garrison orderly-book in his pocket; but he received a flesh wound in the thigh. He slid down a precipice, one hundred feet high, into the ravine between the forts, and escaped to the woods. The governor leaped down the rocks to the river side, where a boat was putting off with a number of the fugitives. The boat crossed the Hudson in safety, and before midnight the governor was with Putnam, at Continental Village, concerting further measures.
Putnam had been completely outmanoeuvred by Sir Henry Clinton. He had continued until late in the morning in the belief that Peekskill and Fort Independence were to be the objects of attack. In the course of the morning he sallied forth with Brigadier-general Parsons, to reconnoitre the ground near the enemy. After their return they were alarmed, he says, by "a very heavy and hot firing both of small arms and cannon, at Fort Montgomery." Aware of the real point of danger, he immediately detached five hundred men to reinforce the garrison. They had six miles to march along the eastern shore, and then to cross the river; before they could do so the fate of the forts was decided.
British historians acknowledge that the valor and resolution displayed by the Americans in the defence of these forts were in no instance exceeded during the war; their loss in killed, wounded and missing, was stated at two hundred and fifty, a large proportion of the number engaged. [Colonel Campbell, who commanded the enemy's detachment, Major Grant of the New York volunteers, and Count Gabrouski, Sir Henry's Polish aide-de-camp, were slain in the assault; their fall exasperated the assailants, who revenged their loss with considerable slaughter.]