At the outbreak of World War I in August 1914, ONI policy was to limit collection to technical information that would assist the Navy in improving the capabilities of the fleet rather than to gather intelligence of an operational nature. ONI had eight officers and eight civilians, and 75 percent of their time was spent in clipping and filing newspaper articles.
Beginning in 1916, the war in Europe induced a rapid expansion in ONI. Counterintelligence, in which ONI had not previously been involved, received the greatest emphasis. It was reasoned that the Allies were already producing intelligence for the support of operating forces, but that the U.S. Navy was very vulnerable internally to German acts of sabotage. Strong security measures were needed quickly.
When the Armistice was declared on 11 November 1918, there were 306 naval reservists plus 18 civil service clerks and messengers serving in ONI. [Beyer comment: It is believed that these numbers do not include the contract special agents assigned to branch intelligence offices.]
Following the war, ONI dropped back to an office force of forty-two in 1920 and returned to its prewar interests in all maritime countries. Most of its counterintelligence responsibilities were terminated.
(Source: Packard, Wyman H., Captain, USN (Ret.), A CENTURY OF US NAVAL INTELLIGENCE, U.S. Government Printing Office, Washington, 1996.)