 The Basic Design Section of the Navy Technical Department decided upon an enlarged and improved Hiryū design with the island on the port side , amidships . After construction of the ships began , the Naval Air Technical Department ( NATD ) began having second thoughts about the location of the island because it thought that the portside location of the island on Hiryū and Akagi had an adverse impact on airflow over the flight deck . Another issue identified was that the amidships position shortened the available landing area , which had the potential to be problematic in the future as aircraft landing speeds increased with their growing weight . To verify these assumptions , the NATD filmed hundreds of takeoffs and landings aboard Akagi in October – November 1938 and decided to move the island over to the starboard side and further forward , about one @-@ third of the length from the bow . Shōkaku was the furthest advanced by this point and the supporting structure for the bridge had already been built ; rebuilding it would have delayed construction so it was left in place . The changes that had to be made consisted of a 1 @-@ meter ( 3 ft 3 in ) widening of the flight deck opposite the island and a corresponding 50 @-@ centimeter ( 20 in ) narrowing on the starboard side and the addition of 100 metric tons ( 98 long tons ) of ballast on the port side to re @-@ balance the ship . 
