An (S-1,S) inventory system with emergency orders

In this paper, the authors develop an approximate model of an inventory control system in which there exist two options for resupply, with one having a shorter lead-time. They assume that demand and the fixed ordering costs are small relative to the holding cost so that a one-for-one ordering policy is appropriate. The authors consider a policy for placing emergency orders that uses information about the age of outstanding orders. They derive the steady-state behavior of this policy and present some computational results.