 While at Hashirajima, "Sōryū"s air group was based ashore at nearby Kasanohara, near Kagoshima, and conducted flight and weapons training with the other First Air Fleet carrier units.Concerned by the US carrier strikes in the Marshall Islands, Lae-Salamaua, and the Doolittle raids, Yamamoto was determined to force the US Navy into a showdown to eliminate the American carrier threat.He decided to invade and occupy Midway Island, an action that he was sure would draw out the American carriers.