In preparation for Operation Olympic, the invasion of southern Kyushu, various figures and organizations made casualty estimates based on the terrain, strength, and disposition of known Japanese forces. However, as reported Japanese strength in the Home Islands continued to climb and Japanese military performance increased, so too did the casualty estimates. In April 1945, the Joint Chiefs of Staff formally adopted a planning paper giving a range of possible casualties based on experience in both Europe and the Pacific. Given a troop list of 766,700 men and a 90-day campaign, the US Sixth Army could be expected to suffer between 149,046 casualties (including 28,981 dead and missing) under the "European Experience" (0.42 dead and missing and 2.16 total casualties/1,000 men/day) and 514,072 casualties (including 134,556 dead and missing) under the "Pacific Experience" (1.95 dead and missing and 7.45 total casualties/1,000 men/day). This assessment included neither casualties suffered "after" the 90-day mark (US planners envisioned switching to the tactical "defensive" by X+120), nor personnel losses at sea from Japanese air attacks. In order to sustain the campaign on Kyushu, planners estimated a replacement stream of 100,000 men per month would be necessary, a figure achievable even after the partial demobilization following the defeat of Germany. As time went on, other US leaders made estimates of their own: