<P> In 1924, General William L. Mitchell produced a 324 - page report warning that future wars (including with Japan) would include a new role for aircraft against existing ships and facilities . He even discussed the possibility of an air attack on Pearl Harbor, but his warnings were ignored . Navy Secretary Knox had also appreciated the possibility of an attack at Pearl Harbor in a written analysis shortly after taking office . American commanders had been warned that tests had demonstrated shallow - water aerial torpedo attacks were possible, but no one in charge in Hawaii fully appreciated this . And in a 1932 fleet problem, a surprise airstrike led by Admiral Harry E. Yarnell had been judged a success and to have caused considerable damage, a finding corroborated in a 1938 exercise by Admiral Ernest King . </P> <P> Nevertheless, because it was believed Pearl Harbor had natural defenses against torpedo attack (e.g., the shallow water), the Navy did not deploy torpedo nets or baffles, which were judged to inconvenience ordinary operations . As a result of limited numbers of long - range aircraft (including Army Air Corps bombers), reconnaissance patrols were not being made as often or as far out as required for adequate coverage against possible surprise attack (they improved considerably, with far fewer remaining planes, after the attack). The Navy had 33 PBYs in the islands, but only three on patrol at the time of the attack . Hawaii was low on the priority list for the B - 17s finally becoming available for the Pacific, largely because General MacArthur in the Philippines was successfully demanding as many as could be made available to the Pacific (where they were intended as a deterrent). The British, who had contracted for them, even agreed to accept fewer to facilitate this buildup . At the time of the attack, Army and Navy were both on training status rather than operational alert . </P> <P> There was also confusion about the Army's readiness status as General Short had changed local alert level designations without clearly informing Washington . Most of the Army's mobile anti-aircraft guns were secured, with ammunition locked down in armories . To avoid upsetting property owners, and in keeping with Washington's admonition not to alarm civil populations (e.g., in the late November war warning messages from the Navy and War Departments), guns were not dispersed around Pearl Harbor (i.e., on private property). Additionally, aircraft were parked on airfields to lessen the risk of sabotage, not in anticipation of air attack, in keeping with Short's interpretation of the war warnings . </P> <P> Chester Nimitz said later, "It was God's mercy that our fleet was in Pearl Harbor on December 7, 1941 ." Nimitz believed if Kimmel had discovered the Japanese approach, he would have sortied to meet them . With the American carriers absent and Kimmel's battleships at a severe disadvantage to the Japanese carriers, the likely result would have been the sinking of the American battleships at sea in deep water, where they would have been lost forever with tremendous casualties (as many as twenty thousand dead), instead of in Pearl Harbor, where the crews could easily be rescued, and six battleships ultimately raised . </P>

Why did united states seize pacific islands during ww2