The silhouette of the USS Carl Vinson is seen yesterday from the Vietnamese city of Danang, where the 103,000-tonne aircraft carrier and two other US ships began a five-day visit. The arrival of the aircraft carrier marks the biggest US military presence in Vietnam since 1975. But it also illustrates Hanoi's complex and evolving relationship with Beijing over the disputed South China Sea. Vietnamese envoys had been working for months to ease the concerns of their giant Chinese neighbour over the visit and the prospect of broader security cooperation between Hanoi and Washington, according to diplomats and others familiar with the talks.