During this time she sank two German blockade runners and was responsible for rescuing many crewmen whose ships had been sunk by Axis submarines and merchant raiders.

On 8 September 1926, the Chief of Naval Operations, Admiral Edward W. Eberle, along with the Commanders in Chief of the United States Fleet and Battle Fleet, and their subordinate commanding officers, the Secretary of the Navy, Curtis D. Wilbur, ordered that all mines and the tracks for laying the mines be removed from all of the Omaha-class cruisers, the working conditions had been found to be very "wet".

[5] The lower torpedo tube mounts, which had also proved to be very wet, were removed and the openings plated over before the start of World War II.

[5] Not satisfied with Melville's suitability as a flagship, Rear Admiral Sumner E. W. Kittelle, Commander Destroyer Squadrons, sought a replacement.

[5] Omaha fell into a routine of operations along the Pacific coast, Central America, and exercises in the Caribbean, with occasional trips to Pearl Harbor.

After removing as much as possible in an attempt to lighten the ship the salvagers employed tugs to pull on Omaha while destroyers circled around them to create waves.

On 28 May, Omaha would return to Norfolk, before leaving on 22 June, for Lisbon, Portugal, and her new assignment as flagship of the temporary Squadron 40-T, which had been formed to protect US civilians and interests in Spain, during the Spanish Civil War.

[5] Task Force (TF) 3, which was at the time commanded by RADM Jonas H. Ingram, had initiated patrol operations out of the ports of Recife and Bahia, Brazil, on 15 June 1941.

On 30 June, with the propulsion and engineering issues having been resolved, Omaha steamed out of Brooklyn, to begin her Neutrality Patrols between Brazil and Ascension Island, which was part of the British Overseas Territories at the time.

Omaha was tasked with enforcing a blockade against Germany by intercepting, boarding, and inspecting vessels that may have been German merchants or agents conducting trade in the region.

Omaha and the destroyer Somers, TG 3.6, which were positioned far northwest of the stated siting at that time, were tasked with supporting the Royal Navy ships.

On 6 November, as Omaha and Somers were en route back to Recife, returning from a 3,023 mi (4,865 km) patrol in the equatorial waters of the Atlantic, smoke was spotted, at 05:06, on the horizon.

As Omaha approached the ship, which was flying US colors with the name Willmoto, out of Philadelphia, identifying her on her stern, she began taking evasive action.

[12] On 7 December 1941, Omaha was steaming with Somers from San Juan to Recife, when she received a communication that informed her captain that the Japanese had attacked the Pacific Fleet at Pearl Harbor.

Omaha's boarding party found Ensign John F. Kelly, USNR, from the US freighter Lammot Du Pont, along with six members of her armed guard detachment and eight crewmen.

On 22 August 1942, while Omaha was waiting for her harbor pilot to take her in at Montevideo, Uruguay, her crew were able to observe the rusting hulk of the German cruiser Admiral Graf Spee that had been scuttled almost three years earlier on 18 December 1939, after the Battle of the River Plate.

When Omaha had moored, a Brazilian naval officer visited Captain Chandler and informed him Brazil was preparing for a formal declaration of war against both Germany and Italy.

One day, as she was at anchor in Carenage Bay, Trinidad, one of her sailors had returned from an especially "hard liberty" and found a spot on Omaha's direction finder deck to sleep off the effects.

This incident brought Captain Chandler to order that Omaha's boarding party's return to wearing the older style life jackets that had proven themselves effective even though they were more cumbersome and bulky.

The damage was determined not to be serious enough to halt their mission and the two cruisers, after completing their patrol, put into Rio de Janeiro for the needed repairs at the Brazilian Navy Yard.

While patrolling out of Recife, with Jouett on 4 January, one of Omaha's aircraft spotted a ship about 55 mi (89 km) northeast of the Brazilian coast.

This time Omaha fired two warning shots over the unknown ship's bow, due to the fact that it appeared that she was dead in the water.

Captain Tillson then allowed members of the crew to rotate topside to observe the gunfire since many of the men were unable to view the action against Rio Grande the previous day.

[5][16] Omaha was out patrolling with Memphis and Jouett on 6 February 1944, when the ships were given orders to be on the lookout for the survivors of a U-boat that had been sunk earlier in the day near their location.

The occupants were German sailors that had survived the sinking of their boat, U-177, that had been sunk by a Consolidated PB4Y-1 Liberator from Bombing Squadron (VB) 107 that was operating out of Ascension Island.

[5] On 4 July 1944, Omaha got underway to the European Theater with destroyer escorts Marts, Reybold, and troop transport General W. A. Mann.

[5] Omaha departed the assault area on 27 August 1944, and returned to Palermo, before getting underway to Oran, Algeria, with Cincinnati, Marblehead, Quincy, and the destroyer McLanahan.

A break in this routine occurred when she returned to the North Atlantic while escorting the transport General M. C. Meigs in company with the Brazilian Marcílio Dias-class destroyers Mariz e Barros and Marcilio Dias to Gibraltar.

Because the proper safety stops had not been installed on the gun he was able to inadvertently fire into a rack of live depth charges that were positioned on the fantail of the ship.

[5] Following the sinking of Bahia, Omaha continued to serve in the South Atlantic, until 12 August, two days after the Japanese announced their intention of surrendering under the terms of the Potsdam Declaration, when she departed Recife, for the last time.