What advice code indicates that a requested item will only suffice and should not be substituted or backordered?

The advice code that indicates a requested item will only suffice and should not be substituted or backordered is 2B. This means that the requisitioner is making it clear that they need this specific item and are not amenable to receiving an alternate or waiting for the item if it is not immediately available. This code helps ensure that the procurement process respects the specific needs of the requester, avoiding potential complications that might arise from substitutions or delays.

In contrast, other advice codes have different implications, such as allowing substitutions, backordering, or indicating that serviceable items are acceptable. This specificity provided by the advice code 2B is crucial in maintaining the integrity and reliability of supply chain operations within military logistics.