Thanks for the response. I believe the Rabbi you were thinking of was Rabbi Kalonymus Kalman Schapira, who was rebbe of the Warsaw ghetto. Incidentally, I recently picked up his mussar sefer, Chovath haTalmidim a few weeks ago. It was in our beit midrash. The introduction includes a somewhat lengthy biography piece about the rabbi, but this is an Art scroll produced book. There is mention made of his other work Aish Kodesh, and I immediately wanted to read it (we don't have it here). But his feelings about the uprising are not mentioned. I was wondering, is this mentioned in Aish Kodesh, or in some other work about the Warsaw ghetto that you would recommend? I was curious where you learned that he approved of it.
The mussar text is pretty good.