It's in two volumes. Volume 1 is called "The Hunters" and covers the 1939-1942 era. Volume 2 is called "The Hunted" and goes from 1943-1945. I got the first volume at our local library on a "for sale" table, and is in excellent condition, while my copy of volume 2 was ordered through Amazon (check the used books... often you can find excellent copies at a significantly cheaper price).
Incidentally, Blair does destroy some common myths about the U-Boats in the introduction to his book. You'll have to read it to see about these.