§ 287c. The subsoil beneath the bed of the Open Sea requires special consideration on account of coal or other mines, tunnels, and the like, for the question is whether such buildings can be driven into that subsoil at all, and, if this can be done, whether they can be under the territorial supremacy of a particular State. The answer depends entirely upon the character in law of such subsoil. If the rules concerning the territorial subsoil[591] would have analogously to be applied to the subsoil beneath the bed of the Open Sea, all rules concerning the Open Sea would necessarily have to be applied to the subsoil beneath its bed, and no part of this subsoil could ever come under the territorial supremacy of any State. It is, however, submitted[592] that it would not be rational to consider the subsoil beneath the bed of the Open Sea an inseparable appurtenance of the latter, such as the subsoil beneath the territorial land and water is. The rationale of the Open Sea being free and for ever excluded from occupation on the part of any State is that it is an international highway which connects distant lands and thereby secures freedom of communication, and especially of commerce, between such States as are separated by the sea.[593] There is no reason whatever for extending this freedom of the Open Sea to the subsoil beneath its bed. On the contrary, there are practical reasons—taking into consideration the building of mines, tunnels, and the like—which compel the recognition of the fact that this subsoil can be acquired through occupation. The following five rules recommend themselves concerning this subject:—
[591] See above, §§ [173], 175.
[592] See Oppenheim in Z.V. II. (1908), p. 11.
(1) The subsoil beneath the bed of the Open Sea is no man's land, and it can be acquired on the part of a littoral State through occupation, starting from the subsoil beneath the bed of the territorial maritime belt.
(2) This occupation takes place ipso facto by a tunnel or a mine being driven from the shore through the subsoil of the maritime belt into the subsoil of the Open Sea.
(3) This occupation of the subsoil of the Open Sea can be extended up to the boundary line of the subsoil of the territorial maritime belt of another State, for no State has an exclusive claim to occupy such part of the subsoil of the Open Sea as is adjacent to the subsoil of its territorial maritime belt.
(4) An occupation of the subsoil beneath the bed of the Open Sea for a purpose which would endanger the freedom of the Open Sea is inadmissible.
(5) It is likewise inadmissible to make such arrangements in a part of the subsoil beneath the Open Sea which has previously been occupied for a legitimate purpose as would indirectly endanger the freedom of the Open Sea.
If these five rules are correct, there is nothing in the way of coal and other mines which are being exploited on the shore of a littoral State being extended into the subsoil beneath the Open Sea up to the boundary line of the subsoil beneath the territorial maritime belt of another State. Further, a tunnel which might be built between such two parts of the same State—for instance, between Ireland and Scotland—as are separated by the Open Sea would fall entirely under the territorial supremacy of the State concerned. On the other hand, for a tunnel between two different States separated by the Open Sea special arrangements by treaty would have to be made concerning the territorial supremacy over that part of the tunnel which runs under the bed of the Open Sea.