Abstract: In an external gunsight viewing apparatus, a housing is provided having a first port coupled to the eyepiece of a gunner's optical sight. A prism is disposed along a common axis between the gunner's eyepiece and a viewing port. The prism folds the image path to an Erfle lens which produces an internal image. The internal image is viewable through a beam combining means, along with a second projected image, folded via a mirror, into the image combining means. A second relay means and additional mirror means direct the combined image along a relay means where they are located along the common axis between the eyepiece and first viewing port.