The company at the center of the U.S. political storm over port security is Dubai Ports World, based in the United Arab Emirates.

DP World is in the midst of a $6.8-billion-bid to buy British-based P&O Ports, which employs about 25,000 people.

P&O - The Peninsular and Oriental Steam Navigation Company - is one of the world's foremost developers and operators of container ports

At stake are 27 terminals that load and unload nearly 22 million containers from ships in ports around the world, including six in the United States.

These containers are about six meters long and typically loaded by a manufacturer or other shipper, lifted by crane onto a truck or train for the trip to a port.

At the port, huge highly-specialized cranes lift the heavy containers easily and stack them aboard cargo ships for the voyage to another nation.

At the next port, the process is reversed, and the containers are then moved by ground transportation to the customer.

DP World would operate the terminals where the loading takes place. Most U.S. ports have several such terminals operated by various companies, many of which are foreign-owned.