Nachi 1928:
The original design for the class called for eight 7,9-inch (200mm) guns in 4 twin turrets, four 4,7-inch (120mm) in single mounts for AA purpose, and 6 twin sets of fixed torpedo tubes, but by the times the four ships where laid down tough the main guns where increased to 10 in 5 turrets, the 4.7-inchers becomes 6 and the torpedo tubes where rearranged in 4 triple sets, still fixed; a catapult offest to starboard was fitted and two Nakajima E2N1 floatplanes composed the cruisers airwing.
Despite not beign the lead ship of the class Nachi was completed in november 1928, 5 months before any other ship and almost 8 before Myoko. Nachi was infact commissioned so early for a mere political reason, her construction was hasted in order to be present for the Emperor Hirohito's (Showa) upcoming Coronation Naval Review to be attended by warships from Great Britian and other countries; so offically Nachi was commissioned on november 26th 1928 and attended the december 4th Coronation Review as scheduled, but she was instead quite far from completion. No catapult and neither Nakajima E2N seaplanes where on board, the main gun director was also not already fitted on top of the bridge, moreover one of the late-changes made to the Myokos while they where under construction was not already fitted, the shelter deck extension abreast the bridge and the fore funnel; this particular feature was added to make up for the loss of crew space after the twelve (six on each side) fixed torpedo tubes initially not supposed to be carried in the preliminar design where added in four triple sets above the engine room.
Myoko 1930:
Lead ship of the class, she was completed to the planned design, with the shelter deck addition. During her fist years of operation she still not carried the planned Nakajima E2N but a single Yokousa E1Y, wich was too heavy to be operated by the Kure type 1 Catapult fitted on board, so it had to be lowered in the water every time.
Haguro 1932:
After a few years of service, the Myokos had the fore-funnel raised in height in order to keep smoke away from the bridge structure, also the 120mm guns recieved protective shields.
Myoko 1936:
Shown after her first main modernization, wich resulted in having a different appearance from that of her siters; the HA director tower fitted abreast the aft-funnel was not moved, bridge modification where less extensive with the 60cm signaling seachlight not relocated and the older directors not beign replaced at the top of the fire control platforms, the airwing is composed by Kawanishi E7K and Nakajima E8N and two Kure type 2 catapults replaced the single type 1 one, the light anti-aircraf armament by two quadruple 13mm machine guns placed abreast the fore-funnel and two 7.7mm lewis machine guns placed on sponsons abreast the bridge structure, moreover the openings for the fore quadruple torpedo tube launchers where already there, Nachi had them too but not Ashigara and Haguro.
Ashigara 1937:
between 1934 and 1935 all the four ships where refitted and modernized, the fixed torpedo tubes and 4,7-inch guns where removed and replaced by eight 5-inch guns in twin mounts and 2 rotating quadruple mounts of torpedo launchers fitted in newly built sponsons on the upper deck; the single catapult was also removed and replaced by two more powerful ones fitted above the torpedo tubes, the cruisers can now carry up to 4 seaplanes, altough the usual complement was three. Ashigara was refitted more extensively than Myoko, recieved a type 94 main gun director fitted with a 6 meter rangefinder on top of the bridge and the manmast derrick was replaced by a stronger built-up one in place of the former pole one.
To compensate for the increased loads and mantain stability the original smaller bulges near the blige keel where extended up by plating up vertically from their outer edges to almost the upper edge of main armour belt in order to raise the ship's dispacement.
Ashigara 1937 at the Spithead Coronation review:
In 1937, in occasion of King George VI coronation, Ashigara represented Japan at the Royal Navy Fleet Review off Spithead on may 20th, future friend and foe German Panzerschiff Graf Spee and US battleship New York where also present
Nachi 1941:
by 1941 a second reconstruction was implemented, the torpedo tubes where increased to 16 in four quadruple banks, now modified to fire the famous Long Lance torpedoes, foremast and mainmast where modified and light AA armament was further argumented with the addition of more 25mm twin mounts; seaplane complement now consisted in three Nkajima E8N, the bulges where further enlarged to maintain stability after the increase in displacement.
Myoko 1942:
even after her second refit Myoko looked different from her sisters, the type 94 main gun director and the 6 meter rangefinder where fitted separatedly on top of the bridge structure and the 3,5 meter rangefinders fitted on both sides of the bridge where removed, the HA rangefinder fitted abreast the aft-funnel was moved forward and a machine gun director added in it's place, a degaussing cable added and the Mitsubishi F1M2 floatplane embarked.
Myoko 1944:
by 1944 Myoko was fitted with type 21 air search radar on the mainmast, two type 22 surface search radar abreast the rangefinders and fire control directors and a type 13 air search on the mainmast, AA armament was also increased to 4 triple, 8 twins and 20 single 20mm machine guns; two searchlights where also landed.
Nachi 1944:
Other than having the type 13 air search radar fitted on the foremast and not having a separate rangefinder mount sported a different Anti-air suite composed by 10 twin and 24 single 25mm machine guns; like myoko she also landed two searchlights.
Haguro 1944:
In late 1944 Haguro anti-aircraft suite was composed of 4 triple, 8 twin and 18 single 25mm machine guns, and other than having the type 13 air search radar on her mainmast like Myoko she differs from all other sisters because the two afmost pairs of torpedoes where removed in order to gain more space for transport equipments and supplies.
Ashigara 1944:
Radar suite was the same as Myoko and Haguro, anti-aircraft armament consisted of 10 twin and 28 single 25mm machine guns.
Haguro 1945 :
Beinn with Ashigara the only survivor IJN cruiser stil capable of moving under her own power in the waters around Singapore (Takao and Myoko where damaged beyond repair and used as anti-aircraft floating platforms) Haguro was relegated to a mere supply ship for Japanese troops still stationed in Indochina; all torpedoes where landed in order to maximize usable space for transport supplies, troops and equipments, B turret had no guns as they where never repaired after beign destroyed during the Philippine campaign, no more seaplanes where carried, 6 triple and 8 twin 25mm machine guns remains on board at the time of her sinking.