At $73.4 billion, fuel will top the list of US exports in 2011, marking the first time in 60 years that we were a net exporter of gasoline, diesel and jet fuel.

The news is generating a lot of headlines, but more surprising to me is number four on the list, an export category that appears to consistently rank in the top five, year after year: Vacuum tubes.

Really? The US exported $37.1 billion worth of vacuum tubes this year? I didn't even know the US still manufactured vacuum tubes anymore, let alone was a major exporter. Where are we shipping them? The 1950's?

A cursory Google search didn't turn up much useful information, so could somebody who knows something about this please explain the US's massive vacuum tube industry to me?