this was done, the attack plan itself was written primarily by Rear Admiral Ryunosuke Kusaka with assistance from Captain Genda and Deputy Chief of Staff, Captain Kameto Kuroshima. Yamamoto had become acquainted with Genda in 1933 when he served aboard the carrier . Yamamoto initially conceived of a one-way attack on Pearl Harbor from away. In his scheme, returning aircraft would ditch in the ocean off Oahu and the pilots would be picked up by destroyers and submarines. Yamamoto was focused on smashing the U.S. Pacific Fleet and sinking as many battleships as possible. Conventional American and Japanese naval doctrine, reflecting the Mahan theory, held that battleships were the instrumental tool of naval supremacy, so it was believed that the destruction of several of these ships would shift the balance of naval power in Japan's favor. In summer 1940 at the age of 36, Genda was chosen by the Japanese Naval Department to travel abroad as a military attaché to obtain first-hand military accounts of German air offensives and British defensive measures during the Battle of Britain. His assessment of the Royal Air Force (RAF), Hawker Hurricane Mk I and Supermarine Spitfire Mk I fighters against the German Messerschmitt Bf 109E "Emil" later provided evidence that the Japanese Mitsubishi A6M Zero Model 21 could easily outmaneuver these Western European aircraft. The carefully recorded details were secretly documented during his brief tour in London and were hand-carried by Genda during his return trip to Japan for naval department studies. His official trip was in accord with British-Japanese naval accords authorizing official military attaché visits to the war front to observe and document military operations. Genda's Western European trip provided added stimulus for Japanese strategic naval studies and exercises to discover weaknesses and formulate tactics that were later used against the U.S. On his return to Japan, he was assigned to the First Carrier Division and met with Yamamoto in early February 1941, during which time Yamamoto presented some ideas for attacking the U.S. Pacific Fleet. Genda warmed to his ideas. Genda had previously considered an attack on Pearl Harbor in 1934 and had discussed the possibility then with Takijirō Onishi. Genda emphasized to Yamamoto that "secrecy is the keynote and surprise the all-important factor." Genda felt that the task was "difficult, but not impossible" and began working on the details of the plan. Genda favored a three wave attack using six