However, after the United States entered World War I on 6 April 1917, the Navy decided to buy Isabel, which it viewed as being not only highly suitable for use as a patrol vessel but also having characteristics similar to those of a destroyer.

[1][3] Arriving at Boston, Massachusetts, on 2 January 1919, Isabel remained inactive at Philadelphia, Pennsylvania, until 25 April 1919, when she was ordered to Key West, Florida, to report to the commanding officer of submarine USS K-5 (SS-36) for duty as a tender to ships on the Mississippi River.

Departing Key West on 14 May 1919, Isabel steamed up the Mississippi to St. Louis, Missouri, stopping at every major port on the river along the way to perform recruiting duties for the Navy.

[3] Returning to New Orleans, Louisiana, on 20 August 1919, Isabel was soon underway for Rockaway Beach, Long Island, New York, for duty as a tender for the famous flying boats of the NC-4 flotilla.

One idea was to convert her into a seaplane tender to support the NC flying boats; another was to send her to Constantinople in the Ottoman Empire to replace the gunboat USS Scorpion (PY-3) as station ship there.

Isabel also took part in the Nanking Incident on 24 March 1927, when shelling and threats of force procured the release of a large group of American and British prisoners held by Chinese nationalists in Nanjing.

[2] In December 1941, as the threat of war with Japan grew ever larger, Isabel was given a secret mission by President Franklin D. Roosevelt to make a reconnaissance of the coast of Japanese-occupied French Indochina.

[citation needed] Isabel's first wartime duty was to escort U.S. Navy submarines through the minefields off Corregidor as they sortied from Manila Bay to defend the Philippines.

[5] For the next month Isabel operated as an antisubmarine escort for convoys in the East Indies, as outnumbered American, British, Australian, and Dutch forces tried desperately to oppose the Japanese offensive.

[3] On 20 January 1942 the ship was part of the covering force at Ratai Bay on the Sunda Strait during the transfer of 3,456 personnel from the liner Aquitania, considered too valuable to risk within enemy land based air range, to smaller vessels for onward transport to Singapore.

[6][note 4] On the way back from a convoy assignment on 7 February 1942, Isabel was sent to rescue survivors from the Dutch merchant ship Van Cloon, which had been sunk by torpedoes and gunfire from a Japanese submarine, near Surabaya, Java.

The torpedo missed, and Isabel quickly drove the submarine down with gunfire and assisted a patrolling Dutch Catalina flying boat in dropping depth charges to drive it from the area.

[2][3] By the time all ships were ordered to leave Java strong Japanese forces under Admirals Kondō and Nagumo were operating south between the islands and Australia.

[3] Isabel had been considered for post-war service as flagship for the Philippine Sea Frontier, but the United States Seventh Fleet commander deemed her to be in too poor condition for such use.