Although Germany held a significant edge over England in optical instrumentation during WWII, the British were not without their bright spots. The firms of Ross (London) and Barr & Stroud (Glasgow) represented the backbone of Her Majesty’s optical expertise,and they rose to the occasion inproducing a wide array of critical military instruments. Ross in particular was also very innovative, developing a distinctive porro-II prism design that improved light transmission over conventional porro-I designs then in service. Ultimately, the result was two of the longest lived binoculars in the British armed forces: the No. 5, and the legendary Mk IV offered here. Developed especially for open sky surveillance, the Mk IV features a unique 5x40 configuration that provides for an exceptionally wide and bright field of view. The oversized rubber eyeshield serves to eliminate extraneous wind and light, and top nitrogen ports (painted red) allow for nitrogen purging to eliminate the fog-prone oxygen otherwise present in the optical path. Focusing is fixed and adjusted for infinity to accommodate viewers with normal eyesight, and its compact size and unusual brightness make it an absolute pleasure to use. Each unit also includes a vulcanized rubber finish to the housing, coated optics, assorted RAF markings, neckstrap, and case. In good condition both inside and out, this is a sensational little glass for tracking birds in flight… or anything else. Height: 5.5”; Weight: 22 oz.