They fought with a few light weapons, grim determination against overwhelming odds and:
"They had actually been preparing for this, and had convinced the Germans to let them build 631 air-raid shelters. Bombing was going on all around them, and the Germans needed their slave laborers so, to keep them safe from Allied bombings, the Germans had allowed them to do this. Now the people used those very shelters to fight against the Germans."This article from ARC gives a good background to the uprising.
See photographs of the uprising, which lasted from 19th April to 16th May 1943.