A collectable Periscope sextant Mk 2a calibrated by Fenns of Farnborough. Straight out of Ministry use, this striking Periscope Sextant comes in Aluminium black case with carrying handle. 

Later DC6 era pressurised planes could not use the perspex astro dome bubble fitted in the roof as in the DC4 / Catalina era planes, as the pressurisation would not allow the bubble window, instead they had a special window frame built into the roof near the rear of the flight deck through which a periscope sextant was used. The Periscope measures 42cm in length, the boxed weight and size can be seen below.