The Office of Naval Intelligence (ONI) was established in the United States Navy in 1882 in the wake of the American Civil War. The ONI was established to "seek out and report" on the advancements in other nations' navies.

ONI's position as the naval intelligence arm began in earnest when the United States declared war on Spain in 1898 in revenge for the sinking of the U.S. battleship Maine in the harbor of Spanish-controlled Havana, Cuba. The ONI's powers grew as it became responsible for the "protection of Navy Personnel, censorship and the ferreting out of Spies and Saboteurs."

In 1929 the Chief of Naval Operations made these functions the permanent duties of ONI. During World War II, Naval Intelligence became responsible for the translation, evaluation and dissemination of intercepted Japanese communications. During the Second World War, the ONI had grown significantly with respect to its budget and staff. It was to become important during the Cold War.

The Office of Naval Intelligence is the oldest continuously operating intelligence service in the United States. The nerve center of ONI is at the National Maritime Intelligence Center (NMIC) in Suitland, Maryland.

Bob Lazar, the source of the Area 51 controversy, is a former employee of ONI, a point that many of supporters have fixed upon, saying he was privy to government secrets.