Converted into a collier for duty with the newly established Navy Fleet Train, Leonidas departed New York on 30 May 1898 on a coaling voyage to Key West, Florida, and following her return to Norfolk, Virginia in mid-June, sailed again on the 23rd for Cuba and Jamaica, supplying occupation troops and naval units.

Reactivated on 8 November 1900 she served with the Collier Service, carrying coal to naval ships and stations along the Atlantic coast and in the West Indies through 1908.

Decommissioning at Portsmouth Navy Yard in Kittery, Maine, from 15 February to 11 June 1909, the ship resumed her service as an Atlantic Fleet Auxiliary.

As part of the Caribbean Detachment, Patrol Force, Atlantic Fleet, Leonidas remained in the West Indies until sailing for home 4 September, arriving Portsmouth 30 October.

After the Armistice on 20 November, the tender sailed for home via ports in Italy, the Riviera, and Spain, and escorted a convoy of submarine chasers from the Azores to Bermuda.