Furutaka 1926:
Designed as a scout cruiser and influenced by the british Hawkins the Furutaka class comes out as an heavy cruiser armed with 6 single 7.9-inch (200mm) guns and four single 3.1-inch (80mm) guns, the armament was completed with the addition of three fixed twin sets of torpedo tubes on each side; in ored to operate aircrafts a trainable flying-off platform was fitted on top of the fourth turret.
Kako 1928:
Funnels where raised in 1927 to improve smoke problems int he bridge area, on Kako an unusual rain cap was fitted on the for-funnel but soon the naval staff realized that the layout does not impove the situation, so after a few months the cap was landed and kako modifed in a way more similar to Furutaka; also the vent intakes for the forward boilers situated in front of the bridge where covered in order to protect them from seawater ingestion.
Furutaka 1935:
during the early 30's both ships where modified to improve their fittings: the flying-off platform for aircrafts was removed and replaced with a Type 1 kure catapult, the 4 single 3.1-inch (80mm) guns where replaced by 4 single 4.7-inch (120mm) ones, also a spotting platform for anti-aircraft fire was added on lattice platforms abaft the fore-funnel, another rangefinder was added amidship and the searchlight platforms where raised; finally two 13mm machine guns mounts where added in sponsons abaft the bridge structure and a boat davits was removed in orer to clear deck space for the aforementioned modifications.
Furutaka 1939:
Starting in 1936 for Kako and in 1937 for furutaka the two sister ships entered the navy yards to underwent a massive rconstruction lasting untill late 1937 for Kako and early 1939 for Furutaka; when recommissioned the two ships where completely changed:
the original main armament of six single 7.9-inch (200mm) guns was replaced by six 8-inch (203mm) ones in three twin turrets in a layout akin to that seen on the Aoba class cruisers, the 4.7-inch (120mm) guns where retained, tough their position was altered to make space for the torpedo reloads; torpedo armament was also upgraded, the fixed tubes where all removed and replaced by two quadruple rotating ones placed near the aicraft catapult, wich was also replaced with a newer and more powerful model.
superstructure was almost completely reconstructed, the mainmast moved slighty forward and lowered slighty, the machinery was vastly improved and the aft funnel was reduced in size by rerouting some of the boiler exhausts into the forward funnel; midship superstructure was rebuilt to accomodate a new searchlight platform and the secondary fire-control tower, the bridge structure was enlarged and upgraded with the addition of new rangefinders and fire-control tower, searchlights where fitted on the lattice platforms erected in the first 1930 refit.
For light anti-aircraft armament four twin 25mm machine guns where fitted on sponsons abaft the midship superstructure, while two twin 13mm mounts where placed in front of the bridge, the airwing updated to two E7K floatplanes instead of a single Nakajima E4N wich the Furutaka class ships carried previously; finally anti-torpedo bulges where added to increase stability after the increase of displacement.
Furutaka 1941:
Some slight more modifications where implemented by the start of WWII, mainly by modifying midship superstructure; a director was also added abaft the bridge structure, and a degaussing cable was fitted.
Furutaka 1942:
The only visible modification done on Furutaka by the time of her sinking at Cape Esperance, was revised airwing now composed by a pair of Aichi E13A.
Kako 1942:
Just like it was before their major refit the way to distinguish the two Furutaka class ships was to look at the stram pipes setup on the fore-funnel, as Kako sported a different arrangement.