What’s the difference between an oil rig and a naval base or an aircraft carrier? Very little, politically, in the eyes of China.

The waters of the South China Sea have witnessed a growing set of confrontations between Chinese and Vietnamese maritime forces as China deploys its deep-sea oil drilling rig, Haiyang Shiyou 981, to disputed waters deep in Vietnam’s exclusive economic zone (EEZ). These have now spread to the land as Vietnamese protestors burn factories and stage riots to express their unhappiness with China’s incursion.

The Chinese action is a reminder of Beijing’s expansive claims over the South China Sea. Based on a document produced in the 1940s by the Nationalist government, the “Nine Dash Line” map covers a vast expanse of the South China Sea, reaching almost as far south as Indonesia and abutting both Vietnamese and Filipino shores. The Chinese oil rig is located in what, according to Beijing, is Chinese territory.

And in this regard, China’s claims differ from those of its neighbors. This is not a matter of EEZs and economic exploitation but a matter of national territory. As Chinese premier Li Keqiang reiterated at the National People’s Congress earlier this year, the seas are “blue-colored national soil.” The implication is that China is no more likely to cede or surrender maritime territory than it is to surrender terrestrial claims. Similarly, the head of the China National Overseas Oil Corporation, which owns the Chinese oil rig, has referred to such platforms as “mobile national territory.”

This operation, then, should not be seen solely or even primarily as economic efforts intended to develop hydrocarbons in the South China Sea (of which there is some promise but thus far little reality) but as a political move to underscore China’s claims to this area as national territory.