The custom vacuum tube designed to operate as a repeater in the first transatlantic telephone cable
is a nifty bit of history. Hundreds of them were in use underwater for over 20 years, none of them
failed. AT&T tried to retrieve the cable after it was retired, but it was impractical, so those tubes are
effectively lost. However, a couple of spares survived, and someone is
selling one on eBay(for $995). It's a fun auction to look at the pictures and read the text (even though it shows up as REALLY BIG
on many browsers).