Which of the following was NOT a major accomplishment of the United States under the leadership of Theodore Roosevelt?

The reasoning behind identifying that all listed answers were accomplished under Theodore Roosevelt's leadership is not accurate. Roosevelt's presidency (1901-1909) was marked by significant accomplishments in various areas, such as trust-busting (antitrust laws), the establishment of national parks, and crucial developments in naval power.

However, while Roosevelt did support advancements in the Navy, such as the Great White Fleet's global tour, the specific milestones mentioned regarding the commissioning of the first real destroyer, the establishment of the first naval flight training unit, and the beginning of flight experiments do not align with his presidency.

The first real U.S. destroyer, known as the USS Bainbridge, was commissioned in 1902, but it did not represent a landmark accomplishment attributed to Roosevelt's direct leadership in terms of naval aviation or flight training. Notably, the foundational developments in naval flight training and flight experiments around that time were initiated later and are more closely associated with World War I and the 1920s.

Therefore, select all options correctly attributed to Roosevelt are misleading, as significant steps in naval aviation came post-presidency, leading to the conclusion that not all listed achievements were realized during Roosevelt's time in office.