This is the extremely rare VT-15 known as the 'Duck-Foot' on account of the splayed base connections.
A closer view of the inner construction. The cylindrical vertical anode has a helical grid within. On the right is the filament tension spring.
The underside of the Bakelite base.
Thanks to Joe Gruber for sending the images.
The thin glass tube envelope is 22 mm in diameter, and including the base pins is 76 mm tall.
Reference: Joe Gruber.
Updated November 26, 2020.