The "war time" phrase refers to the war between the five families. And Tom wasn't a good one, because he wasn't cunning enough to forsee the way the other families came at Sonny. Tom was more of a business man, and would have preferred to settle the differences that caused the war, rather than fight it.

From the novel:
Tom: "The other families won't stand for an all-out war. It puts too much heat on everybody."
Sonny: "No more advice on how to patch it up, Tom....you're job is to help me win. Understand?"