Currently (June 2010) the fastest supercomputer in the US (and, indeed, the world) is Jaguar at Oak Ridge National Laboratory. China's Nebulae at the National Supercomputing Center in Shenzhen has a higher theoretical peak performance, but loses out (by a small amount) in real-world tests.
If you mean physically... I'm not aware of any listing. Many distributed computing solutions can grow quite large (though physical size does tend to impact performance to some extent for most problems). Virtual supercomputers such as the Great internet Mersenne Prime Search project or SETI@Home extend literally worldwide.
the US postal service
Answer: Thermoelectric power and irrigation ;)
The largest tube artillery the US uses is the 155mm howitzer. They also use 270mm multiple rocket launchers.
Between 2,000,000 to 2,500,000 million dollars in the US
According to the US Geological Survey, thermoelectric power generation is the largest user of water in the US each year, accounting for more than 40% of total freshwater withdrawals for all uses.
The Archdiocese does
The US is the largest importer China is the largest exporter then Germany then the US
Yes, you will need a voltage converter when traveling from the US to the UK because the UK operates on a 230V electrical system, while the US operates on a 120V system.
The largest state in the US is Alaska
(in the US) There is no law against the amount of computing power you may own, only your wallet.
No. Ireland uses the Euro. The US uses the American Dollar.
No, Alaska is the largest US State.