Original Item. Only One Available. This is an extremely scarce piece of WWI Aviation equipment, an American-made “Aldis” sight used by pilots to aim their machine guns in a dogfight. This is the first example we have ever offered, and it even comes in its original shipping crate with the caps. The sight was mounted onto the plane as shown in the photograph. This is a must-have item for any WWI Aviation collection!

The Aldis was a Collimated Gunsight. Internally, it featured a series of lenses in a sealed tube filed with an inert gas which stopped it fogging up. Collimated means that the shooters eye position is not important in using the sight. On a ring and bead sight, the shooters eye must be exactly behind the rear sight, which needs to be exactly in line with the front sight which needs to be over the target (if its a no deflection shot). As your head is being thrown around by g-forces as you manouver, this can be really hard to do which makes accurate shooting difficult. With the Aldis collimated sight, as long as you place the aiming rings on the target, you'll hit. It doesn't matter if your eye is too high/low or too right/left, the aiming rings will appear where the bullets will hit.

From "British Aircraft Armament Vol 2: Guns and Gunsights", R Wallace Clarke.

The sight tube contained four hermetically sealed collimating lenses, with a graticule in the form of two concentric circles engraved on a plain glass screen. The outer circle gave the deflection needed for a target plane crossing at 161 km/hr (100 mph), and a small circle gave the gun alignment point. On some later models the outer ring was modified to indicate the wingspan of a Gotha bomber at 183 m (200 yds), and with practice pilots found how to use the circle for other aircraft. The lens system gave unity (no) magnification, and ensured that the ring was always centred on the axis of the sight no matter where the eye was placed. The ideal eye distance from the rubber eyepiece was 127 mm (5 in), which gave a FOV (field of view) of 20 degrees. The anti-oil flap was operated by a cable to the cockpit, where a ring was hooked to a small bracket; when unhooked, the shutter sprang open, giving a clear view. If the shutter was left open, oil fouling would occur, so it became standard practice to fit both Aldis and ring and bead sights. In the first installations the windscreen was cut away in the top right-hand corner, but factory-installed sights passed through a hole drilled in the screen.

The sight features a large rubber eyepiece that is removable and can be placed on either side of the sight. With the eyepiece, it measures 28¾” long. The text on the side of the sight reads:

SIGNAL CORPS, U.S.A. UNIT SIGHT, TYPE-A.
SERIAL NO. 15521 ORDER NO. 20531 - DATE: JAN. 26. 1918

In the box are both caps for the ends of the sight, along with a band that may have been to assist the sight in being mounted. Some small pieces of wood in the box have come off, but it’s still in good shape.

The box is in fair shape and is complete with its original lid, but the nails are all since absent. The box measures 33¾ x 3½ x 4” with the lid on. Written very faintly on on the side of the box is: Mr. F. Marchal / 431 E. Water St. Hartford (City), Indiana. We’re unsure if this was sent back stateside to a friend or relative by a soldier during the war, or if these markings were added later. This would make for a VERY fun research project!

This is one of the greatest pieces of WWI aviation history we have come across, and will definitely become a unique piece of your WWI Aviation collection. We have provided a couple photos for reference in the listing. Comes ready for further research and display!