X-band radar. Your tax dollars at work. Yes, it moves through the water. Patrols an area off the coast of Alaska. It can spot a baseball at 3,000 miles, supposedly. The odd shape is because it's semi-submersible, like some kind of mobile oil rig or something.
We put it out there to keep an eye on that nutjob in North Korea.
Ted - that big tube image I just posted was a huge mercury-arc rectifier. Google "mercury-arc rectifier" and see if your tube shows up in image search.
Did a little more digging. The "354A" is close to the right shape. Hard to tell scale from just this pic **broken link removed** though... Not real obvious that there is actual mercury rolling around inside these either. Now I haveta research "mercury-vapor thyratron". Like I have time for this.. Oh well. Beats "work", I guess.