An aircraft carrier is one of the biggest ships, and here is one (probably American) in Singapore's Changi Naval Base. There are always Singapore police patrol boats and warships on patrol, about one every mile all the way around the country. On the day we saw this carrier there seemed to be even more security than usual. We were once stopped by the Singapore Navy because we came inside their border which is marked by yellow buoys. They were polite but firm, and escorted us back outside their border.