Economics and Operations Research
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Earliest Finish Time
Early British OR
The earliest possible time an activity can be completed without reducing the duration of any of the preceding activities as described in a project network. It is simply the sum of the earliest start time for the activity and the duration of the activity.
Maurice W. Kirby and Graham K. Rand Lancaster University, Lancaster, UK
See ▶ Critical Path Method (CPM) ▶ Network Planning ▶ Program Evaluation and Review Technique (PERT)
Earliest Start Time The earliest possible time an activity can begin without reducing the duration of any of the preceding activities as described in a project network. It is calculated by summing the durations of all activities on the longest path leading to the event that identifies the beginning of the activity.
See ▶ Critical Path Method (CPM) ▶ Network Planning ▶ Program Evaluation and Review Technique (PERT)
The term operational research (OR) was first used in the later 1930s to describe the process of evaluation of radar as an essential aid to the air defense of Great Britain. Emanating from the work of Robert Watson-Watt of the National Physical Laboratory, the novel concept of controlled interception of enemy aircraft by electronic means could only be tested by practical experiment entailing the application of quantitative techniques of analysis. Under the auspices of the Committee for the Scientific Survey of Air Defence, the resulting research program was an outstanding success insofar as the home radar chain proved decisive in more than offsetting RAF Fighter Command’s numerical inferiority during the Battle of Britain in 1940. With its credentials intact as a means of enhancing the effectiveness of an entire military command at a critical stage in the war, OR was thereafter diffused throughout the greater part of the British armed forces both at home and abroad. At the end of the war, in conformity with the experience in Fighter Command, operational researchers, under the leadership of Blackett, regarded as the “father of Operational Research,“could congratulate themselves on their substantial and, on occasion, decisive contributions to the war effort in a number of theaters. In the RAF Coastal Command and the Admiralty, for example, operational
S.I. Gass, M.C. Fu (eds.), Encyclopedia of Operations Research and Management Science, DOI 10.1007/978-1-4419-1153-7, # Springer Science+Business Media New York 2013
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researchers were responsible for a sequence of tactical innovations which led to the defeat of the U-boats in the North Atlantic. For Operation Overlord, moreover, a detailed plan of targets in the French railway system was devised on the basis of quantitative assessment of their capacity for enemy logistical reinforcement, thereby enabling RAF Bomber Command to offer outstanding tactical support to the allied invading forces. With achievement on this scale it is hardly surprising that the advocates of OR should have sought to secure its peacetime future via its diffusion beyond the military sector. In this respect, the per
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