Optimal allocation policy for a multi-location inventory system with a quick response warehouse

We study a multi-location inventory problem with a so-called quick response warehouse and base stock inventory control. In case of a stock-out at a local warehouse, a demand can be satisfied by a stock transfer from the quick response warehouse. We derive the optimal policy for when to apply such a stock transfer, as well as conditions under which that is always optimal. In a numerical experiment we compare the optimal allocation policy to simpler policies.