See also https://en.wikipedia.org/wiki/NATO_Stock_Number

The NATO stock number (NSN) is an identifier used to identify products that are sold armies that are part of NATO or allied with it. This includes various supplies (batteries, personal gear) which are sold in the general market.

The NSN is well defined, with a structure and clear allocation rules, it is useful for products that are not typically identified by a GTIN.

The NSN can be used to group products that have the same specification in cases where GTIN is not available.

Proposal:

• The nsn field is a new field of schema.org/Product that specifies the NSN of the product.

(this proposal came from conversations with colleagues at Google Shopping, who report that this field is widely used in several nations)