"It was on April 19 that the most prolonged Jewish revolt of all took place in the Warsaw Ghetto... With a courage that impressed all who learned of it, 1200 Jewish fighters battled in the streets, apartments, cellars and sewers of the Ghetto. Against these Jews, who possessed only 17 rifles, the Germans brought in 2100 troops armed with machine guns, howitzers and 1358 rifles. Even so, 300 German soldiers were killed, many by hand-made hand grenades, before the revolt was crushed three weeks later."
Gilbert; Martin: Second World War; London, 1989
That's from a comprehensive tome by a world-renowned historian, and though its a while since a read 'Mila 18', the history certainly seems to match up to a lot of what Uris wrote!