Reflector Gunsights used by the US Navy
The Mark VII Illuminated Sight
In 1935, apparently upset by the lack of cooperation of the Air corps, the Navy Bureau of Ordnance designed its first own aircraft reflector sight, the Mk VII. Eight were manufactured by the Naval Gun Factory in 1936-7 for testing and service tests were carried-out in 1938 on F3F-2 aircrafts at NAS San Diego. Tests were apparently conclusive as the Mk VII was eventually put in low production (the Navy still had big hopes in using the AAF N-2A Gunsight). Although close to 600 had been procured by 1941 when production was discontinued, it was never widely used on operational aircrafts.
The Mark 8 all Mods Illuminated Sight
In 1941, the US Navy adopted the British GM2 Gunsight (designated the Fixed gun Reflector Sight Mk II) as the basis of their new standard Gunsight (designated the Mark 8 Illuminated Sight) for fighter and attack planes equipped with fixed forward-firing guns.
The Naval Gun Factory modified the sight, improved its optical qualities and decided to omit the stadiametric ranging mechanism which was found unnecessary and complicated to use. Licence agreements for the production in the US were initially signed with Bell & Howell and Bausch & Lomb (later expanded to the companies Kollmorgen Optical and American Cystoscope) and from early 1942 onwards, the Mk 8 was gradually fitted to every fighter and attack plane in the Navy inventory.
Mark 8 Mod 0 up to Mod 8 Illuminated Sight
First of the series, the Mark 8 Mod 0 & Mod 1 used a flat blackened glass reticle which, because the outer rays were not in focus, presented a distorted pattern[i]. These reticles also did not resist well to the heat produced by the new more powerful bulbs being used. As a consequence, from the Mod 2 onwards, the glass reticle was replaced by a stronger concave copper reticle.
Mark 8 Mod 2 up to Mod 8 were basically similar, differences between Mods being only due to slight internal variations, minor changes in optics and/or optics manufacturers and gradual improvements in manufacturing techniques[ii].
All Mods could either be used with or without a fixed reflector glass (in which case the reticle was projected directly on the armored glass windscreen or to a reflector glass fixed directly on the windscreen) or with an Adjustable Reflector head for rocket firing and/or toss bombing.
After WW II, The Mark 8 was gradually replaced by the newer Mk 1 Sight Unit in attack planes and the Mk 23 Gun sight and Mark 8 Sight Unit in fighters. By the early fifties, the Mk 8 Illuminated Sight was only to be found on the following Navy planes : F4U-4, F8F-1 and the few remaining F6F-5 Hellcats, TBM-3 ASW Avengers, AF-2S Guardians and finally P2V-2 to P2V-4 Neptunes.
[i] Naval Airborne Ordnance – NAVPERS 10826 – Page 209
[ii] Pilot and Gunner Operated Sights – NAVORD OD 9239 – Page IS8
Mark 8 Mod 9 Illuminated Sight (experimental)
The Mk 8 Mod 9 was an experimental modification of the basic Mk 8 Sight with the addition of an externally mounted pendulum assembly which indicated to the pilot when his aircraft was in a skid. The indication was transmitted to the pilot by rays of light directed through a slit in a shutter mounted above the reticle.
Mark 8 Mod 10 Illuminated Sight (experimental)
This Gunsight was the first attempt to modify the basic Mk 8 Illuminated Sight, which had a fixed reticle, into a movable-reticle type; therefore eliminating the need of an adjustable reflector head to adjust the Sight line for rocket firing or skip bombing.
An elevation control lever on the front of the Sight controlled the movable-reticle mechanism and allowed the reticle to be moved plus or minus 60 mils in elevation.
Although this Sight is classified as experimental only in Navy technical documentation, it was fitted at least to some of the first few Douglas A2D-1 Skysharks manufactured (see photo below) and a small production run must at least have been ordered as such a preserved sight produced by Specialities Inc. bears the serial number 63 (see photos below).
Mark 8 Mod 12 Illuminated Sight
This Sight, an improved version of the Mk 8 Mod 10, was also a collimating sight of the movable-reticle type. It was not fitted with crash pad and fixed reflector plate and used the armored windshield of the aircraft as a reflector plate. The elevation control dial on the Sight contained a fixed detent for the zero position and two adjustable detents to help the pilot in making rapid, predetermined, Sight line offsets. The reticle could be moved plus or minus 76 mils in elevation. A dimmer rheostat and a filament selector switch (the bulb contained two filaments operating on 24 to 28 volts) were also part of the sight but were furnished separately.
The Mk 8 Mod 12 was last produced in 1952. Less than 600 were built and were fitted to some AD-5N and AD-6 Skyraiders, to Douglas F3D-1 and F3D-2 Skyknights (as a stop-gap measure while waiting for their Mk 20 Mod 0 Gunsights) and some of the very few A2D-1 Skysharks that were built.
Mark 8 Mod 13 Illuminated Sight
Last of the series, the Mod 13 was identical to the Mk 12 except that it was equipped with a 200-mil day-night reticle pattern, a crash pad and a classic fixed reflector plate.
Only 45 were produced and it’s doubtful if any was ever fitted to an operational aircraft.
The Mark 9 all Mods Illuminated Sight
Also adopted from the British in 1941, the Mark 9 Gunsight was based on the Barr & Strout GJ3 Free Gun Sight (designated the Standard Turret and Free Gun Sight Mk III). It was mass produced by the Wollensak Optical Co. (and later American Cystoscope) and equipped, from 1942 onwards, virtually every Navy plane fitted with turret(s) and/or flexible gun position(s). It was also used as a fixed Sight for toss bombing and rocket firing, together with the adjustable reflector Mk 3 and a different reticle, in attack planes (mostly the PV-2 Harpoon, the P2V-1 Neptune and the P4M Mercator) were space restrictions did not allow the use of the Mark 8 Gunsight.
The Sight consists of a easily removable bakelite case containing the light bulb, a cylindrical middle section for the optics, a hood assembly holding and protecting the reflector plate, and a dimmer switch assembly.
All Mods were identical in appearance. They only differed in the operating voltage of the lamp or in the optics employed. The following mods were produced:
- Mk 9 Mod 0: basic sight operating on 24 volts
- Mk 9 Mod 1: same as Mod 0 but operating on 12 volts
- Mk 9 Mod 2: upgraded Mod 0 with better optics giving almost complete color correction and greatly reducing parallax errors, especially on the outer ring of the reticle pattern.
- Mk 9 Mod 3: same as Mod 2 but operating on 12 volts.
The Mark 10 Illuminated Sight
I have absolutely no info on this Gunsight and must say I’m not even sure it was an aircraft and not an anti-aircraft Gunsight. It is referenced in the Navy OD 1200 manual on optical instruments but, unfortunately, the page relating to this sight is missing from the copy held by the National Archives.
The Mark 20 all Mods Illuminated Sight
The sight was fitted with an horizontal turntable, located in the focal plane of the optical system, that contained three different reticles and light filters. Reticle selection was simply done by rotating a control knob (or in later mods by thumb pressure directly on the turntable) located above the crash pad. The three reticles and corresponding light filters were:
- a Night reticle of reduced pattern and light intensity;
- a classic “ladder type” Day reticle as night fighters and attack planes could also have to operate in day time;
- a Combination reticle to be used under low or medium visibility conditions that occur during dawn, twilight or heavily overcast weather conditions.
The following versions were produced or designed:
- Mk 20 Mod 0: fitted with crash pad but no reflector plate (used aircraft windshield as reflector plate). Reticle control knob located above crash pad.
- Mk 20 Mod 1: identical to Mod 0 except that it was equipped with a fixed reflector plate and no crash pad. Classified as experimental only.
- Mk 20 Mod 2: identical to Mod 0 except that it was equipped with a fixed reflector plate and that the reticle control knob and pinion have been removed (reticle selection done by thumb pressure directly on the gear teeth of the turntable). Experimental use only.
- Mk 20 Mod 3: identical to Mod 0 except that it was equipped with an adjustable reflector head. Experimental only. Served as the production prototype for the Mod 4.
- Mk 20 Mod 4: improved version of the Mod 0 and fitted with an adjustable reflector head to permit the Sight line to be offset in elevation. Offset is done through rotation of the control dial at the left-hand side of the Gunsight. The dial is graduated in mils and sight line can be offset from +75 mils to -350 mils in elevation. The reflector head also provides a detent position for the zero Sight line and two adjustable detents for predetermined offsets. This Mod was the most produced of all the Mk 20 Gunsight versions.
The Mark 20 Mod 0 Sight was fitted mostly to Douglas Skyknights (F3D-1 and F3D-2); the Vought F4U-5N(L) Corsair and finally Grumman F7F-3N Tigercat and F8F-2N Bearcat. The Mark 20 Mod 4 was used mostly on Douglas Skyraiders (A4D-N, AD-5, AD-5N, AD-6) but also Grumman S2F-1 and some Air Force planes (see separate page on Air Force Sights).
The Mk. 24 Mod. 0 Gunsight
Another mystery Gunsight totally unknown to me (until one, unfortunately de-militarized, appeared on Ebay a couple of years ago) on which i have found absolutely no information or reference anywhere. It is based on a Mark 8 Mod 7 and has a moveable reticle. But what makes this Gunsight quite unique in that it has a manual horizontal lead adjustment 0 to 10 mils from left to right for targeting lead and a pneumatic elevation/depression system. Probably developped (produced?) for side firing aircrafts like the AC-47 and AC-119.
The Mk. 1 all Mods Sight Unit
Another early post WWII development of the Mark 8 Illuminated sight, the Mk. 1 Sight Unit is of the movable-reticle type (therefore eliminating the need of an adjustable reflector head to adjust the Sight line for rocket firing or skip bombing) consisting of an optical system and a reticle servo assembly. The reticle assembly is suspended by track guides in the focal plane of the optical system and moves along the fore-and-aft axis of the Sight Unit. Movements for or aft of the optical center-line will elevate or depress the projected reticle image. The Adjustments in elevation (from + 75 mils to – 75 mils) are made by a servo motor fixed to the sight and actuated by a detent –equipped dial on a separate control box (control box Mk. 18).
The following versions were designed and/or produced
- Sight Units Mk. 1 Mod 0 & 1: developed for experimental use only from the Torpedo Director Mk 30 Mod 4 (itself another development of the Mark 8 Illuminated sight);
- Sight Unit Mk. 1 Mod 2: Experimental only. Base model of the Mk. 1 series. Still fitted with a Mk 30 Torpedo director fixed reflector Head;
- Sight Unit Mk. 1 Mod 3: Identical to the Mod 2 except that it was fitted with a classic Mark 8 fixed reflector Head and that a crash pad was added;
- Sight Unit Mk. 1 Mod 4: Identical to the Mod 3 except that it was not equipped with a reflector plate;
- Sight Unit Mk. 1 Mod 5: Identical to the Mod 4 except that the crash pad has been deleted.
Even if the Mk. 1 could also be used in fighter planes, it was only fitted to attack planes and only the Mod 4 (Martin AM-1 Mauler and Douglas AD-1, -2 & -3 Skyraider) and Mod 5 (Douglas Ad-4 Skyraider) saw extensive service use.
The Mk. 1 Sight Unit was part of the Aircraft Sight system Mk 1 which included the sight Unit, a Mk 18 Control Box to control the servo mechanism of the Sight Unit and a Mk 4 Relay Unit.
Other Gunsights used or developed
This section, that will probably never be thorough, will be completed if & when information or documentation is found.
Mk 30 all Mods Torpedo Director
Not actually a Gunsight but nonetheless included here as it could also be used as a Sight for firing fixed guns or dive bombing. The Mk 30 Torpedo Director was another development of the Mark 8 Illuminated Sight used to solve to sight-angle problem for directing the launching of torpedoes from an aircraft. It consisted of a sight housing, optical system, lamp housing, inclinometer, reflector plate assembly with flipping sun filter and, most importantly, a mechanical computing mechanism. Two types of reticle patterns (day & night) were available for use with the Torpedo Director. The fixed Reflector could used be replaced if needed by the Adjustable Reflector Mk 1 Mod 1.
When the Torpedo Director was used for torpedo launching, three parameters had to be entered by the pilot into the Director: Track angle, target’s speed and speed of the torpedo to be used. As a result of these imputs, the fixed reflector and its mounting ring were turned in azimuth through the correct lead angle necessary for the torpedo to hit the intended target.
All Mods (Mod 1 up to 5) were basically the same and only differed in the optical characteristics of the lenses used by its various manufacturers and the ways these lenses were mounted.Librascope Reflector Gunsight used in early Douglas Skyhawks.
In the early fifties, the Librascope Co. designed a Reflector Gunsight that was used in the early versions of the Douglas A4D Skyhawk. This Sight had been in production since about 1953 and the quantities manufactured probably numbered into the thousands. Up until 1969 only a few subtle changes had been made such as, moving the turn and bank indicator up to the bottom of the reflector plate for improved visibility and changing the reticle pattern (probably partial instead of complete circles, and vertical and horizontal radii). In 1969 major changes were made in the mils depression knob, reflector plate support strut, locking lever, etc. by the Naval Avionics Facility, Indianapolis, Indiana. They produced a number of kits for modifying the old sights to the new configuation. In 1970, these changes were incorporated into new sight production.
I am not aware of this Sight being used in any other operational Navy aircraft but i would gladly be proven wrong.
Mk 5 all Mods Sight Unit
This Sight Unit was experimental only. The Mod 0 & 1 never went beyond the drawing board and only twelve units of the Mod 2 were produced for experimentation and performance evaluation.
The Mk 5 was designed as a general purpose (for fixed guns but also rockets and bombing) Gunsight without any computing mechanism but working in conjunction one or more separate fire-control computers. The Sight provided two reticles; a fixed 100 mils fixed reticle and a 6 mils moving reticle. The 6 mils moving reticle established a sight line which was automatically offset both in azimuth (from + 10° to – 10°) and elevation (from +5° to – 10°) by amounts determined by one or more of the fire-control computers.
Mk 6 all Mods Sight Unit
Experimental only. Also designed and produced (Mod 1 & 2 only) for experimentation and performance evaluation only.
The Mk 6 was designed as an universal reflector type Sight (for fixed guns, rockets and bombs) without any internal computing mechanism but working in conjunction one or more separate fire-control computers. The Sight provided two reticles; a fixed 100 mils fixed reticle and a 10 mils moving reticle. The 10 mils moving reticle established a sight line which was automatically offset both in azimuth (from + 10° to – 10°) and elevation (from +5° to – 15°) by amounts determined by one or more of the fire-control computers. When lead-angle signals were generated by one of the fire-control computers, a gimbaled mirror within the Sight Unit was tilted in azimuth, elevation or both. This caused the moving reticle image to shift its apparent position to indicate the point of aim. Motion was produced by means of separate azimuth and elevation motors which positioned the gimbaled mirror.
Mk 7 Mod 0 Sight Unit
Experimental only. This sight was of the fixed-reticle type and was designed to furnish the pilot, via two reticle disks and a pointer, with altitude and dive angle readings as well as skid indication.
Rochester “figure-4” S- series Reflex Sights
The “figure-4” Sights, the S-1, S-2 and S-3, were developed in response to the need to replace the US Navy Mark 8 which was expensive to produce and still optically unsatisfactory as its lens had large parallax and chromatic errors and the illumination was both insufficient and uneven.
The principle of the “figure-4”, in fact an inverted figure 4, was to use a lens of moderate focal length and fold the optical path with two plane mirrors (please see one of the photos below). The name “figure-4” comes from the shape of the optical path.
The S-1 Sight was designed to accommodate a 70 mils reticle with center dot and single ring and an aperture of 3.5 in. A working model was built and submitted to AAF Material Command in august 1942 for testing. Results were very satisfactory and the S-1 Sight was adopted and finally produced, in a modified from, as the AAF N-9 Gunsight.
The S-2 Sight was designed for the Navy to accommodate a reticle pattern with a radius of 150 mils. A few sights were made by the Preston Laboratories for the Navy Bureau of Ordnance. But the sight was rather bulky and was finally rejected.
The S-3 was designed for the Navy as a solid sight. It consisted of a single glass lens and a large prism of plastic with one lens surface. The optical path, lens aperture and dimensions of the Sight were roughly the same as in the S-1. Samples built by the Preston Laboratories were tested by the Navy Bureau of Ordnance and the results were unsatisfactory as it was found it was impossible to obtain thick plastic blocks of sufficient optical homogeneity.
Mid 1942, the Navy Bureau of Aeronautics requested a Gunsight for night use for the F4U-2 equipped with radar. The Sight was to present at infinity the radar oscilloscope screen, airspeed indicator and gyro horizon in addition to the reticle for night shooting. With such a Sight, the pilot would be able to track, intercept and close with the enemy until he made visual contact without having to look away from his Gunsight.
The optical system was arranged in two levels (see drawing below) with the radar tube at the bottom and the airspeed indicator, gyro horizon and reticle on the upper level. The Flightsight was delivered to the Bureau of Aeronautics in April 1943 but, for unknown reasons, was not tested until August 1944 when installed in a JRB aircraft. The sight performed well but, by that time, the need for such a Sight had vanished and the project was abandoned.
Polaroid f/1.6 Sight
Designed with a plastic optical system to be interchangeable with the Mark 8 Sight. It had an aperture of 3.5 in and the optical system was folded once by means of a mirror. The lenses were mounted as a complete unit in a plastic sleeve which slipped into the cast magnesium housing of the Sight. The Sight was tested, but never adopted, by the Navy Bureau of Ordnance.