Unified field theory classical field theory and, two years later, that of Theodor Kaluza, who extended General Relativity to five dimensions. Continuing in this latter direction, Oscar Klein proposed in 1926 that the fourth spatial dimension be curled up into a small, unobserved circle. In Kaluza–Klein theory, the gravitational curvature of the extra spatial direction behaves as an additional force similar to electromagnetism. These and other models of electromagnetism and gravity were pursued by Albert Einstein in his attempts at a classical unified field theory. By 1930 Einstein had already considered the Einstein–Maxwell–Dirac System [Dongen]. This system is (heuristically) the super-classical [Varadarajan] limit
Unified combatant command unified combatant commands is legally mandated in Title 10, U.S. Code Sections 161–168. The Unified Command Plan (UCP) establishes the missions, command responsibilities, and geographic areas of responsibility of the unified combatant commands. As of May 2018, there are ten unified combatant commands. Six have regional responsibilities, and four have functional responsibilities. Each time the Unified Command Plan is updated, the organization of the combatant commands is reviewed for military efficiency and efficacy, as well as alignment with national policy. Each unified command is led by a combatant commander (CCDR), who is a four-star general or admiral. CCDRs exercise combatant