Now that Sherman had connected to the Navy fleet under Rear Admiral John A. Dahlgren, he was able to obtain the supplies and siege artillery he required to invest Savannah. On December 17, he sent a message to Hardee in the city:
I have already received guns that can cast heavy and destructive shot as far as the heart of your city; also, I have for some days held and controlled every avenue by which the people and garrison of Savannah can be supplied, and I am therefore justified in demanding the surrender of the city of Savannah, and its dependent forts, and shall wait a reasonable time for your answer, before opening with heavy ordnance. Should you entertain the proposition, I am prepared to grant liberal terms to the inhabitants and garrison; but should I be forced to resort to assault, or the slower and surer process of starvation, I shall then feel justified in resorting to the harshest measures, and shall make little effort to restrain my army—burning to avenge the national wrong which they attach to Savannah and other large cities which have been so prominent in dragging our country into civil war.
– William T. Sherman, Message to William J. Hardee, December 17, 1864, recorded in his Memoirs
Hardee decided not to surrender but to escape. On December 20, he led his men across the Savannah River on a pontoon bridge hastily constructed of rice flats. The next morning, Savannah mayor R. D. Arnold rode out to formally surrender, in exchange for General Geary's promise to protect the city's citizens and their property. Sherman's men, led by Geary's division of the XX Corps, occupied the city the same day.
Sherman telegraphed to President Lincoln,
"I beg to present you as a Christmas gift the City of Savannah, with one hundred and fifty guns and plenty of ammunition, also about twenty-five thousand bales of cotton."
On December 26, the president replied in a letter:
Many, many thanks for your Christmas gift—the capture of Savannah. When you were leaving Atlanta for the Atlantic coast, I was anxious, if not fearful; but feeling that you were the better judge, and remembering that 'nothing risked, nothing gained' I did not interfere. Now, the undertaking being a success, the honour is all yours; for I believe none of us went farther than to acquiesce. And taking the work of Gen. Thomas into the count, as it should be taken, it is indeed a great success. Not only does it afford the obvious and immediate military advantage; but, in showing to the world that your army could be divided, putting the stronger part to an important new service, and yet leaving enough to vanquish the old opposing force of the whole—Hood's army—it brings those who sat in darkness, to see a great light. But what next? I suppose it will be safer if I leave Gen. Grant and yourself to decide. Please make my grateful acknowledgements to your whole army—officers and men.