1) The ammunition supply for the Aoba and Furutaka classes was three complete rounds per gun per minute while that for the other classes could provide a maximum of four complete rounds per gun per minute.  As loading was at a fixed angle and the elevation speeds were relatively slow, the rate of fire slowed at higher elevations to a maximum of 3 rounds per minute at +55 degrees and 2 rounds per minute at +70 degrees.

2) When it came time for Furutaka and Kako to be rearmed in the 1930s, production difficulties held up deliveries of the 20 cm (8") 2 GÔ guns intended for these ships.  Rather than wait for these guns to be completed, the Japanese instead took 20 cm (7.9") 1 GÔ guns removed from Haguro and Ashigara, rebored and relined them to 20.3 cm (8"), and then installed them onto Furutaka and Kako.  I would assume that these guns would have been replaced with standard 20 cm (8") No. 2 weapons during any regunning operations during the war.

1) IS is my abbreviation for the incendiary shrapnel round (sankaidan) intended for AA use.  This was officially listed as a Common shell, but was actually an incendiary fragmentation round.

2) The propellant charge was in two bags.

3) Type 91 shells were all 6 / [infinity] crh with boat tail and two copper driving bands.  The diameter of the bourrelet was 7.96 in (20.218 cm).  These 20 cm (8") Type 91 shells were not true "APC" projectiles as they lacked a cap, having only a cap head and windshield.  Cap head and windshield together weighed 17 lbs. (7.7 kg).  There were true APC projectiles, designated as Type 91 Mod 1, but these were used only for armor penetration experiments and were not in service.

4) The Shômeidan B Illumination round had an effective range of 17,500 yards (16,000 m) and an illuminating power of 1.6 million candelas.  The maximum ballistic range was 24,900 yards (22,770 m).

5) In addition to the projectiles listed above, there were also Type 91 Exercise and Type 91 Timed Exercise shells.

6) According to "Japanese Cruisers of the Pacific War," the average maximum range for the 10-gun cruisers for daylight actions increased from about 16,840 yards (15,400 m) in 1924 to greater than 21,870 yards (20,000 m) by 1937 and the estimated hit projection increased from 3.0% at 21,870 yards (20,000 m) in 1930-34 to 6.0% in 1935-1940.  The actual percentage of hits achieved during the war was much lower than these figures, a not unusual experience.

   Aoba (3):  Modified Model C
   Myôkô (5):  Modified Model D
   Takao class except Maya (5):  Model E
   Maya (5):  Model E₁
   Furutaka (3):  Model E₂
   Mogami (5):  Mogami Model (also known as Modified E₂)
   Tone (4) and Ibuki (5):  Model E₃

1) These mountings varied in detail from class to class and even within a class but many features were the same.  They were operated with very noisy electric motor driven oil hydraulic pumps located in the revolving structure.  Damage to rubber covered wiring by oil leaks was a common complaint.  Run out was by compressed air.  Elevation was by rack and pinion on the Model C, D and E₁ mountings and by hydraulic actuators on the other Model E mountings.  The Modified E₂ and the Model E₃ mountings had 315 inch (8 m) rangefinders, the other Models had 236 inch (6 m) rangefinders.

2) During modernization and replacement of the 20 cm (7.9") No. 1 guns with the 20 cm (8") No. 2 guns, the Furutaka class was converted from six Model A single mounts to three Model E₂ twin mounts.  Although externally these looked like the Model E mounts, internally the gunhouses and ammunition supply arrangements including hoists resembled the Model C mountings used on the Aoba class.

3) When converted to the No. 2 guns, the Model C and Model D mountings were modified to increase their maximum elevation to +40 degrees.  Some accounts infer that Aoba was later modified to increase maximum elevation to +50 degrees.

4) The Modified E₂ turrets used on the Mogami class had a larger diameter roller path than the other Models in order to fit the larger diameter roller path used for the 15.5 cm guns turrets.  These turrets were also somewhat longer than the other Model E gunhouses.  As the 20 cm guns were longer than the 15.5 cm guns they replaced, the guns of No. 2 turret could not depress below +12 degrees when trained on the centerline.  Otherwise, they would have struck No. 1 turret.  Taking these two items into account, it would appear to be a myth that these ships were designed from the start with the potential for mounting 20 cm guns.

5) The Model E and Model E₁ mountings had two shell hoists per gun, while all other Models had one.  The second hoist was intended to support anti-aircraft firing by making it easier to change ammunition types, but they resulted in a larger turret trunk, a larger lower chamber, increased turret weight and added crewmen.  As loading was performed at +5 degrees and the training and elevation speeds were relatively slow, the reality was that these mounts were of little use for anti-aircraft defense.  The maximum elevation of the Model E was +70 degrees, but the elevating and recoil mechanisms proved to be fragile and it was found that +55 degrees was the maximum practical elevation.  The other Model E mountings were designed for a maximum elevation of +55 degrees.

6) The hull and barbettes of the Tone class had already been completed up above the armored deck when the main armament was changed from triple 15.5 cm turrets to twin 20 cm turrets.  As the twin 20 cm turret needed a smaller diameter roller path than the triple 15.5 cm turret, this meant that the diameter of the completed portion of the barbettes was now too large for the twin 20 cm turrets.  To compensate, the design for the top of the barbettes was altered to a conical shape with a diameter of 18.7 feet (5.70 m) at the lower level and 16.4 feet (5.00 m) at the upper level.  The follow-on Ibuki class were to use the same E₃ turrets as the Tone class, but these later ships were designed from the start with 16.4 foot (5.00 m) diameter barbettes.  However, the distance between the centerlines of No. 1 and No. 2 barbette on the Ibuki class was the same as for the Mogami class, which meant that the guns in No. 2 turret still needed to be raised in order to clear No. 1 turret (see Note 4 above).

7) The gun axes were 74.8 in (190 cm) apart for all Models.

8) As originally completed in the 1920s, the Model C and Model D mountings used pusher hoists for the powder charges that effectively created a continuous powder train between the gun breeches and the magazines.  These powder hoists were replaced by bucket hoists in 1930s which gave improved protection from flash.  Shell hoists remained pusher types.  Flashtight doors were fitted to all shell and powder hoists at both the lower and upper ends.  Revolving flash tight scuttles were fitted between the magazines and powder handling rooms.  These changes did slow the supply of ammunition to four charges per minute.  However, the new arrangements proved their worth when a flareback wrecked Turret No. 2 on Ashigara in the summer of 1935.  Although 41 men were killed or injured, the flash did not penetrate down into the magazines.  Model E mountings also incorporated these improvements.

9) Model E mountings (and the Model B mountings used on Akagi and Kaga) differed from earlier mountings in having flat instead of sloped roofs and in that the rangefinders were partially within the mounting instead of being superimposed.  The entry doors on the rear of these Model B and Model E mountings had a curved top while the doors on the earlier Models were rectangular.

10) Model C, Model D and those Model E mountings with one shell hoist per gun had a crew of 19 in the gunhouse, nine in the shell room and ten more in the powder magazine.  Those Model E mountings with two shell hoists per gun had a crew of 23 in the gunhouse and more in the shell rooms.