What action should be taken for importing an unclassified defense article for improvement before reexport?

The appropriate action for importing an unclassified defense article for improvement before reexport is that the District Director of Customs will permit it without a license. This is based on regulations that govern the import and export of defense articles, which distinguish between classified and unclassified items.

Since the article in question is unclassified, it does not fall under the strict licensing requirements that apply to classified materials. The involvement of the District Director of Customs allows for a more streamlined process, providing that the defense article meets specific criteria that ensure it is within the legal capacity to be imported and subsequently improved before reexport.

In contrast, the other actions listed would generally apply to classified materials or more sensitive transactions that necessitate a higher level of oversight and approval. For example, submitting an export license application, notifying the Directorate of Defense Trade Controls, or obtaining approval from the Department of Defense pertain primarily to regulated items requiring stringent compliance measures and documentation, not applicable in this case of unclassified items.