The RAF sent 800 bombers on the night of Feb 23 and interestingly enough the USAAF sent another 400 B-17s the next day to give them another going over. The whole idea was to deliver a knockout blow so that Germany would immediately surrender. Unfortunately they chose to fight on for another three months.
Also remember that the allied forces in Europe were experiencing enormous casualties. One unit of the US army went through 50 Lieutenants from D Day to the surrender of Germany.
There was and is no military justification for bombing civilians. The allied could have bombed the railways, and not the inner city. In addition, everybody knew that the Nazis were never going to surrender, because they wanted the German nation to share their personal fate (death, suicide). He who continues to claim that it was alright to kill thousands of civilians shall explain me why the US Air Force did not the same with Baghdad 2003.