The last named was in command, and on the 22d of August he landed twenty thousand troops, including five thousand hireling Hessians, at Gravesend Bay, with the intention of flanking the Americans out of their positions at Flatbush and the Heights and then advancing across the island to East River and New York.
It was not until two days later that (in the words of a soldier writing to his wife at that time) "General Putnam was made happy by obtaining leave to go over--the brave old man was quite miserable at being kept here," in New York.

Only three days after his arrival the battle was fought, which (in brief) was brought about by the British surprising an outpost at one of the three passes to the American rear, on the night of the 26th of August and thus turning the patriots' position.

With more than three times the numerical strength of the Americans, the British were successful, and the former lost more than a thousand men, most of them made prisoners, including Generals Sullivan and Stirling.
Washington hurried over reenforcements, until there were nearly ten thousand men at the Heights; but Putnam soon found it impossible to conduct its defense against twenty thousand of the enemy, with ten thousand more in reserve, and, with Washington's sanction and cooperation, he withdrew his men from their perilous position by a night retreat across the river, which was a triumph of military sagacity and achievement.

The more than nine thousand men, with their ammunition, arms, provisions, etc., were safely over the river before the British became aware of what was going on.

Then it was too late, and notwithstanding that the Americans had been outflanked and defeated by the most skilful strategy, the British lost the chief fruits of their victory by procrastination.
The loss of Long Island meant, of course, the evacuation of New York, since the city could now be commanded by the enemy's guns on the Heights.