Harry Truman actually said...

This national wealth, like other lands owned by the United States, is held in trust for every citizen of the United States.

The lands and mineral resources in question lie under the open sea off the Pacific, the Gulf, and the Atlantic coasts of our country.

The veto message covers that very ground.

Texas, of course, before it became a State and while it was an independent republic, had whatever rights then existed in the submerged lands...