United States Under Secretary of State

Under Secretary of State (U/S) is a title used by senior officials of the United States Department of State who rank above the assistant secretaries and below the deputy secretary. From 1919 to 1972, the under secretary was the second-ranking official at the Department of State (immediately beneath the U.S. secretary of state), serving as the secretary's principal deputy, chief assistant, and acting secretary in the event of the secretary's absence.

Source: Wikipedia — United States Under Secretary of State (CC BY-SA 4.0)