A new book on Soviet bomber aircraft of World War 2 is available at Aamazon.com titled Soviet Bombers of the Second World War (if you're interested). It contains info about WW2 bomber aircraft developed in the USSR, but also contains info about WW2-era Soviet bomber doctrine and the organization of WW2 Soviet bomber squadrons. While the Pe-8, Pe-2, Tu-2, Il-2, Il-4, and SB are well known among amateur experts on pre-1945 Soviet aviation, the DB-240, Yak-2/4, Su-2, Ar-2, and Yer-2 are less well known.