The continuation of a conventional war would have been much costlier than an atomic attack  The US was planning for a massive invasion of the Japanese Home Islands (Operation Olympic). Nine divisions were to land on the southern Japanese island of Kyushu. However the Japanese had ten divisions in southern Kyushu by August, and 600,000 troops on the whole island. [1]  The US army widely disseminated a figure of half a million casualties for the conquest of Japan. This was however only the figure for public consumption and some calculations went much higher. [2] On top of the US losses the same amount and probably considerably more Japanese deaths would have to be added. The estimates of US losses were so bad that atomic bombs were actually considered for use in clearing the landing beaches.  Chief of Staff George C. Marshall argued “We had to visualize very heavy casualties unless we had enough atomic bombs at the time to supplement the troop action.” [3] Invasion was therefore not really an alternative to the A-bomb use at all. Although the use of the bomb in a battlefield situation might be more justifiable that it was considered shows the ignorance of the radiation effects that might well have been a disaster for US forces as well as Japanese.  [1] Edward J. Drea, ‘Intelligence Forecasting for the Invasion of Japan: previews of Hell, Hiroshima in History: The Myths of Revisionism, (Columbia, 2007) p.59,71  [2] D. M. Giangreco, "A score of bloody Okinawas and Iwo Jimas": President Truman and casualty estimates for the invasion of Japan’, Hiroshima in History: The Myths of Revisionism, (Columbia, 2007), p.88  [3] Edward J. Drea, ‘Intelligence Forecasting for the Invasion of Japan: previews of Hell’, pp.74-5.