In March Chinese ships intercepted and tried to drive off two U.S. Navy ocean surveillance ships operating off Hainan and northern China in international waters. The Chinese leveled the most violent threats against the USNS Impeccable (T-AGOS-23), operating near the new submarine base at Hainan. Her master showed great resourcefulness, using fire hoses to drive off the Chinese ships. To justify their action, the Chinese cited the United Nations Convention on the Law of the Sea treaty, which provides countries with a 200-mile Exclusive Economic Zone (EEZ) but has no impact whatever on the right to operate warships outside the six-mile territorial limit. These incidents can be viewed either as tests of the new Obama administration (which soon assigned a guided-missile destroyer to escort one of the ships) or as a seaborne equivalent to the harassment of the U.S. Navy EP-3E electronic intelligence aircraft early in the Bush administration. At roughly the same time, the Chinese president expressed his "disquiet" over the strength of the American dollar, in effect threatening to destabilize the U.S. economy further by dumping the vast number of dollar-denominated U.S. government bonds his banks hold.