The airplane takeoff platform, part of which mounted atop the number 4 semi-turret, was replaced with a catapult fitted just fore of the No.3 twin turret.

[7] As built the Aoba was more than 900 tons heavier than its design weight, with negative effects on the performance of the ships similar to that of the Furutaka class overweight condition.

To offset the numerical superiority the U.S. Navy enjoyed, the planned upgrades included the latest weapons, protection, fire control systems, and communication equipment.

[9] In the spring of 1930 the two ships had their manually-operated 12 cm anti-aircraft guns replaced with improved electro-hydraulically operated units.

The bridge structure was rebuilt almost identically to the Furutaka class modifications to accommodate the latest rangefinders and fire control equipment for the main battery, antiaircraft and torpedoes.

To prevent the draft from increasing even more, and to improve stability, bulges were added, simultaneously enhancing anti-torpedo protection.