It dealt with intelligence matters concerning British naval plans, and with the collection of naval intelligence in regard to coastal defences, foreign powers, mobilisation, trade and war.

[1] The NID staff were originally responsible for fleet mobilisation and war plans as well as foreign intelligence collection; thus in the beginning there were originally two divisions: (1) intelligence (Foreign) and (2) Mobilisation.

The Trade Division was abolished in October 1909 in the wake of the Committee of Imperial Defence inquiry into the feud between the First Sea Lord, Admiral Sir John Fisher and former Commander-in-Chief Channel Fleet, Admiral Lord Charles Beresford, when it was discovered that the captain heading the Trade Division had been supplying the latter with confidential information during the inquiry.

[3] In 1910, the NID was shorn of its responsibility for war planning and strategy when the outgoing Fisher created the Navy War Council as a stop-gap remedy to criticisms emanating from the Beresford Inquiry that the Navy needed a naval staff—a role the NID had been in fact fulfilling since at least 1900, if not earlier.

After this reorganisation, war planning and strategic matters were transferred to the newly created Naval Mobilisation Department and the NID reverted to the position it held prior to 1887—an intelligence collection and collation organisation.