Nonethess it appeared during the first year of the Pacific War, at least to the American press and public,  that the Fortress had amply demonstrated its effectiveness against naval targets and that it had dramatically fulfilled the expectations of those, such as Billy Mitchell, who had championed high-level bombing as the best method of dealing with enemy ships.

The first great success attributed to the B-17 was the sinking of the Japanese battleship Haruna off Luzon during the invasion of the Philippines, by a Fortress piloted by Colin Kelly, who thereby became one of the first American popular heroes of World War  Two.    Although Haruna had in fact not even been hit,  the story created a deep impression which was never fully corrected.

Similarly, in June 1942 when US carrier aircraft (with assistance from US submarines) inflicted a crushing defeat on the Japanese Navy in the Battle of Midway the laurels were claimed by B-17s of the Army Air Corps.  Again this was accepted by the press and proclaimed in such headlines as "Army Fliers Blasted Two Fleets off Midway."  This was greatly resented in the Navy,  but this mythical account of the Midway battle persisted until the end of the war.

The truth was that the Fortresses based on Midway had persistently and bravely attacked enemy shipping during the battle,  but probably without scoring even one bomb hit.  In fact, as the official historian Samuel Morison notes in the "History of US Naval Operations of World War II"there is no evidence that any Japanese aircraft-carrier was hit by a B-17 during the entire course of the Pacific War.   At Midway Hiryu - one of the crippled and burning Japanese carriers - was strafed by  a B-17 and one of her AA guns was damaged.  This was probably the only damage inflicted by B-17s on any enemy ship during the great battle.

An indication of the relative ineffectiveness of the Fortress in its anti-shipping role is provided by the observation that at Midway the Japanese fighters did not consider it worthwhile to attack the B-17s.  While this in part expressed their respect for the defensive firepower of the Fortress,  it was more an expression of the Japanese contempt for high-level bombing as a method of attack on ships - the Japanese high command,  especially that of the Navy, had never believed in it.

A quotation which expresses this contempt (although it also demonstrates that high-level bombing was not completely ineffective, at least against stationary vessels) follows  - 

[On 25 August 1942 a  Japanese troop convoy bound for Guadalcanal had been attacked by SBD Dauntless dive-bombers of the US Marine Corps and several ships had been hit]

"Another hit on the 9300 ton Kinryu Maru . . . gutted her with fire and brought her to a stop.
Tanaka [the Japanese admiral commanding the convoy and its escort] . . . ordered Mutsuki to close the windward side of the transport to take off her passengers and crew. 

"At 1015 eight Flying Fortresses from Espiritu Santo appeared over Tanaka's force.  Commander Hatano,  Mutsuki's skipper,  glanced up at them and casually returned to his rescue work.

"Consequently,  when the 'Forts' let go a pattern of bombs,  his destroyer was dead in the water.  After three bombs had struck,   she was dead under the water . . . 

"Commander Hatano emerged,  dripping, to remark quaintly that 'Even the B-17s could make a hit once in a while.'  He claimed that his ship was the first to be hit by horizontal bombing during the war."

[S.E. Morison "History of US Naval Operations in World War II"  Vol. V,  pp. 104-5]

Admiral Spruance,  commanding Fifth Fleet at Okinawa,  expressing his respect for the pilots of the Kamikaze Corps,  remarked to members of his staff that they were "at the opposite extreme from our Army heavy bombers,  who bomb safely and ineffectively from the upper atmosphere."

[John F. Wukovits "Admiral Raymond A. Spruance" in "Men of War" (ed. Stephen Howarth)]

The truth was that during the inter-war period and well into World War Two most of the world's major air forces greatly overestimated the accuracy and effectiveness of high-level bombing, whether against shipping or against land targets. 

The extreme rarity of hits on warships ironically underlines the achievement of Billy Mitchell and his men in their demonstrations of the effectiveness of high-altitude bombing  -  later experience showed that their performance,  for example in  the Ostriesland test,  was exceptional.

Nonetheless this is not sufficient to explain the great tactical miscalculation which led to the belief in high-level  maritime bombing.   It does, surprisingly,  seem that little account had been taken of the ability of ships to manoevre out of the way of bombs dropped from high altitude.      The single most important factor in making high-level bombing ineffective was,  simply,  the time-lag between release of the bombs and their arrival at sea level.   By the time the bombs had reached that level  the target would almost invariably be somewhere else,  even if the ship had not taken any specific evasive action  (the aiming technique of the period tended to be inadequate to deal even with the normal deflection of a moving target).

However,  even against stationary targets high-level bombing proved to be far less accurate than the pre-war demonstrations by Mitchell and others would have suggested.  The perhaps superior-to-average  skill of those involved in the demonstrations would not be enough to fully explain the discrepancy. 

Probably the main part of any explanation is that combat conditions  -  i.e.  the threat from fighters and from anti-aircraft gunfire  -  made precise aiming far more difficult than had been anticipated  -  and only real combat experience was likely to show this.