Article 19 or the "Pueblo clause" would devastate U.S. intelligence operations
Most obviously, and possibly what President Reagan's advisors had in mind, coastal states' rights under UNCLOS include the so-called "Pueblo clause." It says that it is not "innocent passage" for any foreign ship in the twelve-mile territorial sea to perform "any act aimed at collecting information to the prejudice of the defense or security of the coastal state" (article 19.c). But American naval vessels underway routinely take soundings and keep their radio receivers turned on, and any coastal state can claim that receiving information about the approaches to a harbor or the configuration of a coast is prejudicial to its security. Although it is possible with some ingenuity to argue that the provision does not mean what it says, foreign states are not bound by the ingenuity of American lawyers. And other provisions of the same article, like the clause forbidding "research or survey activities" (article 19.j) also contain undefined terms that can be interpreted to end American naval rights of passage. Indeed, it is also forbidden to undertake "any other activity not having a direct bearing on passage" (article 19.1). I have never understood how the United States negotiators could accept this language.
Under the convention, the United States assumes a number of obligations at odds with its military practices and national security interests, including a commitment not to collect intelligence. The U.S. would sign away its ability to collect intelligence vital for American security within the “territorial waters” of any other country (Article 19). Further- more, U.S. submarines would be required to travel on the surface and show their flags while sailing within territorial waters (Article 20).