The start of the war led to the dissolution of the treaty system, but the dramatic need for new vessels precluded a new design, so the Clevelands used the same hull as their predecessors, but were significantly heavier.

Following the start of World War II in September 1939, Britain announced it would suspend the treaty for the duration of the conflict, a decision the US Navy quickly followed.

[2] The ship's belt armor ranged in thickness from 3.5 to 5 in (89 to 127 mm), with the thicker section amidships where it protected the ammunition magazines and propulsion machinery spaces.

[3] The ship embarked on her shakedown cruise, first in Chesapeake Bay, and later into the Atlantic, as far south as the Gulf of Paria in Trinidad in the British West Indies.

[4] On 14 December, Wilkes-Barre left Pearl Harbor to join the rest of the American fleet, which was then at its forward anchorage at Ulithi in the Caroline Islands.

[4] During this period, Wilkes-Barre was assigned to the subordinate unit Task Group 38.2, which was centered on the aircraft carriers Lexington, Hornet, and Hancock.

The fleet's aircraft carriers launched a series of strikes against targets on Japanese-occupied Formosa and in the southern Ryuku Islands to neutralize Japanese airfields that might otherwise interfere with the imminent invasion of Luzon in the Philippines.

[4] Reports of Japanese warships off Cam Ranh Bay, French Indochina, on 12 January prompted the American command to detach Wilkes-Barre, the rest of Cruiser Division 17, New Jersey and Wisconsin, and escorting destroyers to form Task Group 34.5 (TG 34.5).

The fast carrier task force then sortied for an attack on Japan, which began on 18 March and targeted the southernmost island of Kyushu.

Wilkes-Barre launched one of her Kingfishers to recover another pair of pilots from the carrier Bunker Hill who had been shot down off Yakushima during the attacks.

American forces began to go ashore on Okinawa on 1 April, and TF 58 continued to support the operation, carrying out strikes on Japanese airfields in the region, including on Kyushu, Shikoku, and southern Honshu.

The ships returned to TF 58 the next day; the fleet was attacked by kamikazes that morning, and two of them struck Bunker Hill, inflicting serious damage.

The cruiser placed her bow in contact with Bunker Hills starboard quarter so some forty men, who were trapped by fires, could climb to safety aboard Wilkes-Barre.

The ship sent additional firefighting equipment aboard the carrier and took of injured men, and by 15:34, the fires had been extinguished, allowing Wilkes-Barre to pull away.

[4] Thirteen men from Bunker Hill had died by 12 May, so a burial at sea was held that day; the remaining survivors were transferred to the hospital ship Bountiful.

Later on the 12th, TF 58 got underway to launch another round of strikes on the Kyushu airfields to further degrade the Japanese ability to interfere with the Okinawa invasion fleet.

During the action, shell fragments, possibly from American guns, struck Wilkes-Barre and wounded nine men on the aft signal bridge.

Wilkes-Barre was detached from the unit the next day to return to the Philippines for repairs and maintenance at San Pedro Bay that lasted from 1 to 20 June.

[4] Wilkes-Barre thereafter rejoined TF 38, again part of TG 38.3, which sortied on 1 July to begin the last major campaign of air strikes on Japan.

On the 14th, Wilkes-Barre and several other vessels were detached to create Task Group 35.1; the unit also included Pasadena, Astoria, and Springfield and six destroyers.

[8] Further carrier strikes were conducted in late July, but bad weather forced the fleet to temporarily withdraw in early August.

The fleet returned to the Japanese coast on 8 August and resumed air attacks on the 9th and 10th, by which time both atomic bombs had been dropped on Hiroshima and Nagasaki.

Wilkes-Barre then returned to Tokyo, laying in Sagami Bay from 12 to 14 September to supervise the demilitarization of midget submarine bases at Aburatsubo and Kurihama.

She stopped in Pearl Harbor on the way to the West Coast of the United States, finally arriving in San Pedro, California, on 31 January.

She stopped in Plymouth in the United Kingdom on 27 February and cruised in British waters over the course of March and April, during which time she sailed to Bergen, Norway.