evidence: The secret hydrographic research during the 1930s allowed naval authorities from different countries to understand this vast maritime territory as an archipelago crossed by secret sea-lanes. The Spratly Islands, long perceived as an area to avoid, were reinterpreted as strategic territory from which a maritime power could control the sea-lanes of the South China Sea. During the Second World War, U.S. submarines based in Australia patrolled the South China Sea and regularly crossed the Dangerous Ground using these internal sea-lanes. They also pursued scientific research around the Spratlys, notably to study layers of high density salt in the water which allowed the American submarines to escape detection by Japanese sonar. [...] The maritime space of the Dangerous Ground is structured by internal sea-lanes, with two main axes (north-south and east-west). The choice of which Spratlys to occupy seems to have followed the logic of control of these internal sea-lanes. Thus, after Taiwan occupied the main island of Itu Aba in 1956, Vietnamese forces garrisoned islands and reefs which control the western entrance of the east-west sea-lane. The Philippines, at the end of the 1960’s, favored control of the northern part of the north-south sea-lane.