While more powerful than existing armored cruisers, the appearance of the British Invincible class in 1908 with their armament of eight 12-inch (305 mm) guns and speed of 25 knots (46 km/h; 29 mph) rendered these ships obsolete before they were commissioned.

They used steam provided by 18 mixed-firing, superheater-equipped Miyabara water-tube boilers, with a working pressure of 17 kg/cm2 (1,667 kPa; 242 psi), that sprayed fuel oil on the coal to increase its burn rate.

Performance during Ibuki's initial sea trials on 12 August 1909 was unsatisfactory as she only reached 20.87 knots (38.65 km/h; 24.02 mph) despite the turbines exceeding their power rating with 27,353 shp (20,397 kW).

The ship ran her full-power trials again on 23 June 1910 and reached a speed of 21.16 knots (39.19 km/h; 24.35 mph) from 28,977 shp (21,608 kW).

[5] The Ibuki-class armored cruisers were armed with four 45-caliber 12-inch 41st Year Type guns, mounted in twin-gun hydraulically powered centreline turrets.

[10] They fired 850-pound (386 kg) projectiles at a muzzle velocity of 2,800 ft/s (850 m/s);[11] this provided a maximum range of 24,000 yd (22,000 m) with armour-piercing (AP) shells.

The intermediate armament was much heavier than the older ships, with four twin-gun turrets equipped with 45-calibre 8-inch 41st Year Type guns mounted on each side.

[13] Defense against torpedo boats was mainly provided by fourteen 40-caliber 4.7-inch 41st Year Type quick-firing (QF) guns, all but two of which were mounted in casemates in the sides of the hull.

[18] Construction of both ships was delayed by a lack of facilities at their shipyards, a shortage of appropriately trained workers and their low priority for building.

In fact, construction on Aki was completely halted for about five months in favor of Ibuki because the former's turbines were late and the cruiser was better suited to serve as the testbed for the new technology.

[22] Ibuki sailed to Thailand in 1911 to represent Japan during the coronation ceremony of King Rama VI Vajiravudh.

[24] The ship was ordered to Singapore and cooperated with the British to hunt down the light cruiser Emden in the East Indies and Indian Ocean.

[26] With the ending of the threat to the convoy, Ibuki was transferred to the Second South Seas Squadron at Truk in the Caroline Islands.

[27] She was refitted at Kure in 1918, disarmed in 1922, and stricken from the Navy List the following year and scrapped in accordance with the Washington Naval Treaty.