Ambassador. . ("Minister Plenipotentiary, Second Class") . ("Minister Plenipotentiary, First Class") ("Ambassador of Spain"): not all Spanish Ambassadors hold this grade, which is limited by law to 3% of the total Corps. United Kingdom His Majesty's Diplomatic Service differentiates between officers in the "Senior Management Structure" (SMS; equivalent to the Senior Civil Service grades of the Home Civil Service) and those in the "delegated grades". SMS officers are classified into four pay-bands, and will serve in the Foreign, Commonwealth and Development Office in London as (in descending order of seniority) Permanent Under-Secretary (O-10), Directors-General (O-9), Directors (O-8), and Heads of department or deputy directors (O-7). Overseas Ambassadors and High Commissioners (in Commonwealth countries) are generally drawn from all four SMS bands (and the D7 delegated grade) depending on the size and importance of the mission, as are Consuls-General, Deputy Heads of Mission, and Counsellors in larger posts. (Deputy Heads of Mission at the most significant Embassies, for example those in Washington and in Paris, are known as Ministers.) In the "delegated grades", officers are graded by number from 1 to 7; the grades are grouped into bands lettered A‑D (A1 and A2; B3; C4 and C5; and D6 and D7). Overseas, A2 grade officers hold the title of Attache; B3‑grade officers are Third Secretaries; C4s are Second Secretaries; and C5s and D6s are First Secretaries. D7 officers are usually Counsellors in larger posts, Deputy Heads of Mission in medium-sized posts, or Heads of Mission in small posts. United States In the United States Foreign Service, the personnel system under which most U.S. diplomatic personnel are assigned, a system of personal ranks is applied which roughly corresponds to these diplomatic ranks. Personal ranks are differentiated as "Senior Foreign Service" (SFS) or "Member of the Foreign Service". Officers at these ranks may serve as ambassadors and occupy the most senior positions in diplomatic missions. The SFS ranks, in order from highest to lowest, are: Members of the Foreign Service consist of five groups, including Foreign Service Officers and Foreign Service Specialists. Like officers in the U.S. military, Foreign Service Officers are members of the Foreign Service who are commissioned by the President. Foreign Service Specialists are technical leaders and experts, commissioned by the Secretary of State. Ranks descend from the highest, FS‑1, equivalent to a full Colonel in the military, to FS‑9, the lowest rank in the U.S. Foreign Service personnel system.