Why did Lincoln send a ship to Fort Sumter in April 1861?

Union troops were about to surrender to the Confederacy.%0D%0AUnion troops were about to surrender to the Confederacy.%0D%0A%0D%0AUnion troops had been attacked by the Confederacy.%0D%0AUnion troops had been attacked by the Confederacy.%0D%0A%0D%0AUnion troops desperately needed food and water.%0D%0AUnion troops desperately needed food and water.%0D%0A%0D%0AUnion troops had run out of ammunition

Union troops had been attacked by the Confederacy.