On the night of the 14th, the parallel was within striking distance of the 2 redoubts closest to the river. If they could be captured and fortified, the British would be in an impossible situation. Two attack forces were assembled for an early evening attack: one French and one American led by Alexander Hamilton. Together the plan was to simultaneously attack the redoubts under cover of darkness in hopes their movement would take the British off guard.
At 8:00 p.m. a French force advanced in columns towards Redoubt #9. As they began the attack they were challenged by a German Hessian: "Wer da?" --Who goes there? With no reply, the 120 German and British troops immediately began to blindly open fire into the darkness. The assault would be over in less than 30 minutes. Seventy-seven French were wounded and 15 killed. The British and Germans lost 18 killed and 50 men were taken prisoner.
Not wanting to give away their position, at the same time as the French assault began, the Americans began their assault on Redoubt #10 with unloaded weapons. Without waiting for the the abatis to be cut down, the Americans crossed over the ditch surrounding the redoubt and swarmed over the parapets. In just 10 minutes they successfully overcame the British holding the position. Nine men were killed and 31 wounded.
As soon as both redoubts were captured, work began extending the second parallel. By the next day the parallel had reached the captured redoubts. Cornwallis realized the position that he was now in was hopeless. It was just a matter of time. He sent word to Clinton:
My situation now becomes very critical; we dare not show a gun to their old batteries, and I expect that their new ones will open to-morrow morning... The safety of the place is, therefore, so precarious that I cannot recommend that the fleet and army should run great risque in endeavouring to save us."
Rather than sit back and wait for the inevitable outcome, Cornwallis ordered an assault against the two redoubts, in hopes that this attack might disable them. Some 350 men attacked the two redoubts and successfully drove off both the French and Americans from their position, leaving the two batteries unprotected. The British immediately spiked the artillery pieces inside, making them of no immediate use. However, a counter attack forced the British back and the guns were operational after a few hours of repair.
The only remaining hope for Cornwallis was abandoning Yorktown and retreating across the river to Gloucester. Boats were still available. Around midnight of the 16th, some light infantry and part of the 23rd Regiment boarded small boats to cross the river. Just as they reached the north side of the river, a violent storm came up and sent the boats so far down the river that they could not be retrieved in time to take any additional troops across the river under cover of darkness. The next day, the boats were retrieved, and used to bring the men back across the river.
At the same time all of the French and American artillery opened fire on the town. The previously erected earthworks were quickly reduced to rubble making them impossible to use for return artillery fire. Whether the earthworks were in tact or not became moot as the British ammunition supplies were exhausted.
On the morning of the 17th, a drummer mounted one of the parapets and began to beat out the cadence for a parley. Although none of the American forces could hear the drum beat, they could see the young man and firing ceased. Once the firing had stopped, an officer holding a white handkerchief came out. As he approached the American lines, he was blindfolded and taken to Washington to discuss surrender terms. The siege was over.