Williamson Manufacturing Co. Ltd. approx. 88-90mm push-on/slip-on fit ORANGE FILTER. NOT SURE about fit, it may slot into front of lens? There is a lug on each side. For AIRCRAFT CAMERA. Excellent quality, good condition, glass is fairly clean, signs of age and some edge speration (should work OK ).......................................

Armed Forces code is 14A/3774 (probably for RAF).