A thick fog clouded the battlefield throughout the day, greatly hampering coordination. The vanguard of Sullivan's column, upon Germantown Road, opened fire upon the British pickets on Mount Airy, just after sunrise at 05:00. The British pickets fired their cannon in alarm, and resisted the American advance. Howe rode forward, thinking they were being attacked by foraging or skirmishing parties, and ordered his men to hold their ground. It took a substantial part of Sullivan's division to finally overwhelm the British pickets, and drive them back into Germantown.
Howe, still believing his men were facing only light opposition, called out; "For shame, Light Infantry! I never saw you retreat before! Form! Form! It is only a scouting party!" Just then, three American guns came into action, opening fire with "grapeshot. Howe and his staff quickly withdrew out of range. Several British officers were shocked to see their own soldiers rapidly falling back before the enemy attack. One British officer later described the number of attacking Americans as "overwhelming". 
Cut off from the main force, Colonel Musgrave, of the British 40th Regiment of Foot, ordered his six companies of troops, around 120 men, to barricade and fortify the stone house of Chief Justice Chew, called "Cliveden. The American troops launched a determined assault against Cliveden, however, the outnumbered defenders repulsed their attempts, inflicting heavy casualties. Washington called a council of war to decide how to deal with the fortification. Some of his subordinates favoured bypassing Clivden entirely, leaving a regiment behind to besiege it. However, Washington's artillery commander, Brigadier General "Henry Knox, advised it was unwise to allow a fortified garrison to remain under enemy control in the rear of a forward advance. Washington concurred.
General William Maxwell's brigade, which had been held in reserve, was brought forward to storm Cliveden. Knox positioned four 3-pound cannon out of musket range to bombard the mansion. However, the thick walls of Cliveden withstood the bombardment from the light field guns. The Americans launched a second wave of infantry assaults, all of which were repulsed with heavy losses. The few Americans who managed to get inside the mansion were shot or bayoneted. It was becoming clear to the Americans that Cliveden was not going to be taken easily. Among this assault was Lieutenant "John Marshall of the Virginia Line, the future "Chief Justice of the United States, who was wounded during the attack.
Prior to Maxwell's futile attack against Cliveden, Sullivan's division advanced beyond in the fog. Sullivan deployed Brigadier General "Thomas Conway's brigade to the right, and Brigadier General "Anthony Wayne's brigade to the left before advancing on the British centre-left.  The 1st and 2nd Maryland Brigades of Sullivan's column paused frequently to fire volleys into the fog. While the tactic was effective in suppressing enemy opposition, his troops rapidly ran low on ammunition. Wayne's brigade to the left of the road moved ahead, and became precariously separated from Sullivan's main line. As the Americans launched their attack on Cliveden, Wayne's brigade heard the disquieting racket from Knox's artillery pieces to their rear. To their right, the firing from Sullivan's men died down as the Marylanders ran low on ammunition. Wayne's men began to panic in their apparent isolation, and so he ordered them to fall back. Sullivan was subsequently forced back, although the regiments fought a stubborn rear-guard action. Since the British units pursuing them were redirected to fight Greene's column, Sullivan's men fell back in good order. 
Meanwhile, Nathanael Greene's column on Limekiln Road had finally caught up with the bulk of the Americans at Germantown. Greene's vanguard engaged the British pickets at Luken's Mill, driving them back after a savage skirmish. The fog that clung to the field was compounded by palls of smoke from the cannon and musket fire, throwing Greene's column into disarray and confusion. One of Greene's brigades, under Brigadier General "Adam Stephen, veered off-course and began following Meetinghouse Road, instead of rendezvousing at Market Square with the rest of Greene's troops. The wayward brigade collided with Wayne's brigade, and mistook them for redcoats. The two American brigades opened fire on each other in the fog, causing both to flee. The withdrawal of Wayne's New Jersey Brigade, having suffered heavy losses attacking Cliveden, left Conway's right flank exposed.
To the north, an American column led by McDougall came under attack by the Loyalist troops of the Queen's Rangers, and the Guards of the British reserve. After a brutal contest, McDougall's brigade was forced to retreat, having suffered heavy losses. Despite the reversal in fortune, the Continentals were still convinced of a possible victory. The 9th Virginia Regiment of Greene's column launched a determined attack on the British lines as planned, managing to break through and capturing a number of prisoners. However, they were soon surrounded by two arriving British brigades under Cornwallis. Cornwallis then launched a counter-charge, cutting off the Virginians completely, forcing them to surrender. Greene, upon learning of the main army's defeat and withdrawal, realised he stood alone against Howe's entire army, and so withdrew.
The primary attacks on the British and Hessian camp had all been repulsed with heavy casualties. Washington ordered Armstrong and Smallwood's men to withdraw. Maxwell's brigade, still having failed to capture Cliveden, was forced to fall back. Howe ordered a pursuit, harrying the retreating Americans for some 9 miles (14 km), though he did not follow up on his victory. The pursuing British forces were finally forced to retire in the face of resistance from Greene's infantry, Wayne's artillery, and a detachment of dragoons, as well as the coming of the night.
Of the 11,000 men Washington led into battle, 30 officers and 122 men were killed, and 117 officers and 404 men were wounded.  According to a Hessian staff officer, some 438 had been taken prisoner by the British, including Colonel "George Mathews and the entire "9th Virginia Regiment.   Brigadier General "Francis Nash, whose "North Carolina brigade covered the American retreat, had his left leg taken off by a cannonball, and died on October 8 at the home of Adam Gotwals. His body was interred with military honours on October 9 at the Mennomite Meetinghouse in "Towamencin.  Major John White, who was shot at Cliveden, died on October 10.  Lieutenant-Colonel William Smith, who was wounded carrying the flag of truce to Cliveden, also died from his wounds.  In total, 57 Americans, over one-third of all those killed in the battle, died in the attack on Cliveden. 
British casualties in the battle were 71 killed, 448 wounded and 14 missing, only 24 of whom were Hessians.  British officers killed in action include Brigadier General "James Agnew and Lieutenant-Colonel John Bird. Lieutenant-Colonel William Walcott of the "5th Regiment of Foot was mortally wounded, and later died. 
"Wyck House served as a hospital during the battle.
Washington's ambitious plan failed due to several factors:
Washington had intended for his attack to be a second "Trenton. Had everything gone according to plan, Washington could easily have trapped and destroyed a second major British force. Coupled with Burgoyne's "defeat at Saratoga, the defeat of Howe at Germantown could have compelled "Lord North and the British government to sue for peace.  While in this sense it was a limited strategic success for the British, the long-term strategic consequences of the engagement favoured the Americans. Howe had, once again, failed to follow up on his success, and allowed Washington to escape with his army, leading to their encampment at Valley Forge.
The battle in particular made a strong impression upon the French court that the Americans would prove worthy allies. "Sir George Otto Trevelyan, in Volume IV of his History of the American Revolution, concluded that, although the battle had unquestionably been a defeat for the Americans, it was of "great and enduring service to the American cause". In particular, the engagement persuaded the "Comte de Vergennes to vouch for the United States against Britain.  He continues:
|“||That the battle had been fought unsuccessfully was of small importance when weighed against the fact that it been fought at all. Eminent generals, and statesmen of sagacity, in every European Court were profoundly impressed by learning that a new army, raised within the year, and undaunted by a series of recent disasters, had assailed a victorious enemy in his own quarters, and had only been repulsed after a sharp and dubious conflict.||”|
"John Fiske, in The American Revolution (1891), wrote:
|“||...The genius and audacity shown by Washington, in thus planning and so nearly accomplishing the ruin of the British army only three weeks after the defeat at the Brandywine, produced a profound impression upon military critics in Europe. "Frederick of Prussia saw that presently, when American soldiers should come to be disciplined veterans, they would become a very formidable instrument in the hands of their great commander; and the French court, in making up its mind that the Americans would prove efficient allies, is said to have been influenced almost as much by the battle of Germantown as by the surrender of "Burgoyne.||”|
Eight Army National Guard units (103rd Eng Bn, A/1-104th Cav, 109th FA, 111th Inf, "113th Inf, 116th Inf, 175th Inf and 198th Sig Bn) and one active Regular Army Field Artillery battalion (1-5th FA) are derived from American units that participated in the Battle of Germantown. "There are only thirty currently existing units in the U.S. Army with lineages that go back to the colonial era.
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Battle of Germantown