Chelsea Ships Bell Tambour #30 1918 USNO United States Naval Observatory. But How many Tambour Mantle clocks do you think went to the USNO? ! Especially with a fancy dial and hands. This must have been in an important office or area. Truly one of a kind. I have never seen a USNO mantle clock. All of the USNO Chelseas I have ever seen are more utilitarian models. As you likely know, the USNO is…