[citation needed] Lisbon and the neighbor Tagus estuary has always been the largest and most important naval base of Portugal, since the 12th century.

[citation needed] During the Age of Discovery, in the 15th and 16th centuries, Lisbon and the Tagus became the major naval base in the World.

In the late 19th century, the idea of building a new naval arsenal at the site of the Royal Estate of Alfeite arose.

[citation needed] Several senior naval officers also began to advocate the idea of concentrating the several Navy facilities in Lisbon and the Tagus, at a single site near the future new arsenal.

[citation needed] Considered one of the largest and best equipped installations of its kind, the Alfeite Arsenal started full operation in 1938.