When the war broke out, she was based in Vladivostok and made several sorties in search of Japanese shipping in the conflict's early months without much success.

The Japanese sank the oldest Russian ship, Rurik, and damaged Gromoboi and Rossia during the subsequent Battle off Ulsan.

Three months after the damage from the grounding incident was repaired, she struck a mine, but successfully returned to port.

Gromoboi was transferred to the Russian Baltic Fleet after the end of the war and began a lengthy refit that was completed in 1911.

Gromoboi was originally intended to be a repeat of Rossia, but a design modification for thicker armour and improved engines made that unfeasible.

[2] As completed Gromoboi trimmed badly by the bow, which reduced her speed and made her very wet forward.

Loads had to be shifted aft and ballast added to the rear of the ship to correct her trim, but she was regarded as a good sea boat afterward with an easy, although rapid, roll.

They fired 193.5-pound (87.8 kg) projectiles at a muzzle velocity of 2,950 feet per second (900 m/s) which gave a range of 12,000 yd (11,000 m) at 13° elevation.

[4] The gun fired 10.8-pound (4.9 kg) shells to a range of about 8,600 yards (7,864 m) at its maximum elevation of 21° with a muzzle velocity of 2,700 ft/s (820 m/s).

[4] They fired a 3.3-pound (1.5 kg) shell at a muzzle velocity of 1,476 ft/s (450 m/s) at a rate of 20 rounds per minute to a range of 2,020 yards (1,850 m).

[4] These fired a 1.1-pound (0.50 kg) shell at a muzzle velocity of 1,450 ft/s (440 m/s) at a rate of 20 rounds per minute to a range of 3,038 yards (2,778 m).

The change in the machinery allowed Gromoboi to dispense with Rossia's glacis armour that had been necessary to protect the tops of the engine cylinders.

The funnel uptakes and ammunition hoists were protected by 1.5 inches of armour between the lower and middle decks.

She left Liepāja on 10 December 1900 en route to the Far East and stopped briefly at Kiel, where she was inspected by Prince Henry of Prussia, and at Plymouth where the officers visited the Devonport naval base.

By this time, Gromoboi was assigned of the Vladivostok Cruiser Squadron under the command of Rear Admiral Karl Jessen.

[15] During the war the bulk of the Russian Pacific Fleet was located in Port Arthur where it was blockaded by the Japanese.

On 10 August, the ships at Port Arthur attempted breakout to Vladivostok, but were turned back in the Battle of the Yellow Sea.

36 miles (58 km) north of the island he encountered the Japanese squadron commanded by Vice Admiral Kamimura Hikonojō tasked to patrol the Tsushima Strait.

The Japanese force had four modern armoured cruisers, Iwate, Izumo, Tokiwa, and Azuma.

[16] Jessen turned to the northeast when he spotted the Japanese at 05:00 and they followed suit, albeit on a slightly converging course.

Jessen turned southeast in an attempt to open the range, but this blinded the Russian gunners with the rising sun and prevented any of their broadside guns from bearing on the Japanese.

About 06:00, Jessen turned 180° to starboard in an attempt to reach the Korean coast and to allow Rurik to rejoin the squadron.

Kamimura circled Rurik to the south at 08:00 and allowed the other two Russian ships to get to his north and gave them an uncontested route to Vladivostok.

They fought a running battle with the Russians for the next hour and a half; scoring enough hits on them to force their speed down to 15 knots (28 km/h; 17 mph).

[18] About 10:00, Kamimura's gunnery officer erroneously informed him that Izumo had expended three-quarters of her ammunition and he turned back after a five-minute rapid-fire barrage.

By this time she had been sunk by Naniwa and Takachiho which had closed to 3,000 metres (3,300 yd) of Rurik in order to finish her off.

Shortly after the Japanese turned back, Gromoboi and Rossia were forced to heave-to to make repairs.

[22] The Russians took this opportunity to reinforce her armament with six more 6-inch guns mounted on her upper deck, protected by lightly armoured casemates.

The trials were run again on 27 July 1911 and were more satisfactory as they developed 13,337 indicated horsepower (9,945 kW) while Gromoboi reached 18.5 knots (34.3 km/h; 21.3 mph).

[3] She engaged the German battlecruiser SMS Von der Tann at the entrance to the Gulf of Finland on August 10, 1915.