Multistage inventory management with expediting

After reformulating Clark and Scarfs (1960) classical serial multi-echelon model so that the lead time between adjacent echelons is one week (period), the option to expedite between each resulting echelon is added. Thus, each week requires a decision to be made at each echelon on how many units to e xpedite in from the next upstream echelon (to be received immediately) and how many to regular order (to be received in one week), with the remainder detained (left as is). The model can be interpreted as addressing dynamic l ead time management, in which the (remaining) effective lead time for each ordered unit can be dynamically reduced by expediting and/or extended Use o f Clark and Scarfs (1960) idea of echelon stocks reduces a complex, multidi mensional stocking problem to the analysis of a series of one-dimensional s ubproblems. What are called rop-do,vn base stock policies, which are readil y amenable to managerial interpretation, ale shown to be optimal. Myopic po licies are shown to be optimal in the stationary, infinite horizon case. Th e results are illustrated numerically.