that was only limited during the era of sailing ships, but also included extensive use of combat engineering in support of the infantry. One of the most extensive and complex of combined operations that followed the war was the Allied intervention in the Russian Civil War that saw forces deployed in the Baltic region, the Arctic region, along the Black Sea coast and in the Russian Far East, which for the first time saw the use of aircraft used in cooperation with the naval and land components of the deployed forces. The phrase "combined operations" was first introduced by the British War Office in World War II to denote multi-service activities, those that involved air, land or naval forces acting together, and coordinated by the Combined Operations Headquarters. Given U.S. usage of the word 'joint' meaning such activities, the British usage faded relatively quickly. After World War II, the United States Department of Defense began using the term to denote multi-national operations, which might mean land forces of several countries, for example Combined Forces Land Component Command, or 'Combined Joint,' multi-national, multi-service activities and operations. The term Combined Joint Task Force then took on an extra meaning, beyond that of a multi-national, multi-service grouping, when it came to refer to a particular type of NATO deployment planning, outside the NATO Treaty area, in the late 1990s. Since the early 1980s the concept of combined operations had been referred to by NATO and in particular by the United States Department of Defence as joint operations. Regardless of the use of combined, joined or interoperability terms the concept is used to ensure that different military organisations maintain the ability to conduct combat and non-combat military operations regardless of the national and service (ground, naval and air forces) differences. The ability to conduct combined operations allows national forces, their subordinated formations, units or systems to perform tasks and complete missions and operations together. The overriding requirement is that they share common doctrine and procedures, utilise each other's infrastructure and bases, and to be able to communicate with each other. These abilities reduce duplication of effort and increase economies of scale in a strategic alliance of its members, allow pooling of resources, and produces synergies among its commands. In the NATO concept, interoperability does not necessarily require common military equipment. What is important is that this equipment can share common facilities and is able