Combined Operations Headquarters was a department of the British War Office set up during Second World War to harass the Germans on the European continent by means of raids carried out by use of combined naval and army forces. Admiral of the Fleet Roger Keyes was the first director, from 17 July 1940 to 27 October 1941, replaced first by Lord Louis Mountbatten and then Major General Robert Laycock (October 1943 – 1947). The main forces used by Combined Operations were the Commandos.
It comprised background staff whose job was to plan operations and to develop ideas and equipment to harass the enemy in any way possible. It also covered all those who worked with landing craft up to and including the landing ships that were used in the various amphibious operations.
The badge of Combined Operations was an eagle over a submachine gun over an anchor, reflecting the three service arms; the Royal Air Force, the British Army and the Royal Navy.
Among the projects undertaken by Combined Operations was the surveying of landing sites for invasions, including those of Sicily and Normandy. These were carried out by Combined Operations Pilotage Parties made up of members of the Royal Navy, Royal Marines, Corps of Royal Engineers and Special Boat Service.
In current military use, combined operations are operations conducted by forces of two or more allied nations acting together for the accomplishment of a common strategy, a strategic and operational and sometimes tactical cooperation. Interaction between units and formations of the land, naval and air forces, or the cooperation between military and civilian authorities in peacekeeping or disaster relief operations is known as joint operations or interoperability capability.
The concept of combined operations evolved largely as a result of expeditionary warfare that can be traced to the Sea Peoples. In its basic form it involved raiding coastal regions by land forces arriving from the naval vessels. The raiding tactics were expanded into more complex operations by Alexander the Great who used naval vessels for both troop transporting and logistics in his campaigns. The next exponents of combined operations in the ancient world of the Mediterranean Basin were the Carthaginians who introduced two entirely new dimensions to the use of naval forces by staging not only operations that combined naval and land troops, but also eventuated in combining strategic multi-national forces during the land phase of the operation when Hannibal in his most famous achievement at the outbreak of the Second Punic War marched an army that included war elephants, from Iberia over the Pyrenees and the Alps into northern Italy. Following the example of Carthage, the Romans used combined operations extensively to expand their Empire and influence in the Mediterranean and beyond, including the Roman conquest of Britain, which was not only a temporary expeditionary operation but included long term occupation and Roman settlement of the territories.