USA(A)F GUNSIGHTS – THE N- SERIES OF REFLECTOR GUNSIGHTS HEADS
The N- series of gunsights (starting with the N-2) had the particularity of having the reflector support (also called sight or sighting head) designed as a separate and removable part of the gunsight assembly. This allowed a great freedom of installation as the reflector support could be reoriented with respect to the sight body (as often seen on N-3 and N-6 for example) but also permitted the sight head to be changed from one model to another
Sighting heads for the N- series can be classified in 5 categories:
- Early AAF procured sight heads not given any specific designation;
- the A- series of “tilting” or variable sight heads;
- the B- series of fixed sight heads;
- the C- series of “tilting” or variable sight heads used in conjunction with radar;
- Sight heads designed and procured directly by aircraft manufacturers.
For any serious collector, identifying, finding and collecting those sighting heads will definitely be the biggest challenge for his collection as, if most gunsights of the N- series are relatively easy to find, the same cannot be said for the sighting heads.
Early AAF procured Sight Heads not given any specific designation
The Air Force designed and procured at least four sight heads together with its N-2/3/5 gunsights. Those sight heads were not given any designation number and were simply identified by Army drawing number.
- A fixed sighting head designed and procured together with the N-2. Drawing number and manufacturer unknown.
- A fixed sighting head designed and procured together with the N-2A. Drawing number and manufacturer unknown. Identical to (1) except for the fixing mechanism now made of two ears clamped together by a nut and bolt.
- A fixed sighting head designed and procured together with the N-3A. Drawing number 41D4892 and manufactured by the Ohio Pattern Works Co. Identical to (2) except that it also included a fixing support for a gun camera.
I believe these three sight heads were designed and procured specifically for fighter use as I have never seen a period photo of such a sight head used together with a fixed gunsight in an attack or light/medium bomber plane. Some were however used in B-24 tail turrets.
These three sight heads, even if designed at the start together with a specific model, were interchangeable and could of course be used with any of the N-2 or N-3 gunsight.
- A fixed sighting head designed and procured together with the N-5. A 2 inches shorter version of (2). Drawing number 41D3024 and manufactured by the Ohio Pattern Works Co. Procured for use in the Martin upper turret together with the N-5 and more than probably N-3 gunsights.
All these heads had the inconvenient of being quite bulky and also obstructive to the pilot vision as the reflector plate was supported and fixed on all four sides.
the A- series of “tilting” or variable Sight Heads
The A- series of sighting heads was developed to allow fixed gunsights of the N- series to also serve for low level horizontal bombing (also called skip bombing) and later rocket firing. In order to do so, the line of sight could be easily and rapidly depressed (by a variation of the angle of the reflector glass) to a desired angle corresponding to a known altitude, speed and type of ordnance to be dropped. The line of sight could also very easily be restored to its “zero” position used for gunnery.
Cam stops located at the back of the graduated knob also allowed the pilots to preset several preferred angles depending on personal choices, experience and known ordnance to be used.
A-1 Sight Head
The A-1 was designed to fit the N-3 series gunsights but could also be used on the N-6 thanks to an adapter ring.
Unfortunately, field reports revealed that its protruding knob was very dangerous for the pilot in case of crash landing (some head wound fatalities were even reported) and the A-2 was therefore developed to replace it.
A-2 Sight Head
However, the A-2 arrived at a time when the tilting feature on fighters was seriously questioned as most field reports explained that fighter pilots were in fact not using the variable head and were always leaving it at zero when skip bombing. Its use was therefore limited to light and medium bombers.
The A-2 was designed to fit the N-3 series gunsights but could also be used on the N-6 thanks to an adapter ring.
A-3 Sight Head
A-4 Sight Head
A-12 Sight Head
The A-12, designed for use with the N-3C, was developed and produced by the Lynn Instrument Co. (the same company that produced the L-3 gunsight). But, unlike the L-3, the A-12 was directly procured by the Government. North American seems to have been the only aircraft manufacturer using the A-12 on its late B-25 and T-6 planes.
The B- series of fixed sight heads
B-1 Sight Head
The B-1 was developed together with the N-9 and became famous (and very collectable today!) as it was used on the early P-51D. Compared to earlier fixed sight heads procured by the Air Force, the B-1 had the advantage to have an inclinometer included and to have the reflector glass only held at the bottom.
B-2 Sight Head
B-3 Sight Head
The B-3 was a slightly scaled-down version of the B-2 designed to fit the N-3 series of gunsight. It was widely used on fighters still equipped with N-3 gunsights when the A-1 “tilting” head was found to be unnecessary but also dangerous to pilots in case of crash landing.
The C- series of “tilting” or variable sight heads used in combination with radar.
C-1 Sight Head
Without the Falcon radar (and therefore no C-1 sight head): The pilot presets the gunsight for a certain range by rotating the adjusting knob on the A-1 gunsight head. As he flies, his line of sight is on the target as seen through the gunsight. When he estimates his range to the target to be equal to the prescribed distance he pushes the firing button. He then quickly resets the sight to a shorter range and repeats. With this technique, about 3 shells can be fired per run. The big trouble is that estimating ranges is tricky practice, so the pilot flies in close where his judgment is better but the flak thicker.
With the Falcon radar (and the C-1 sight head): The radar operator and the pilot, sitting side by side, work as a team. The pilot homes on a target. He motions the operator. When the target becomes visible the operator is ready. Watching it on his 6000 yard range sweep he begins tracking, keeping the range step lined up with the left hand side of the target echo by turning a crank on the side of the indicator unit. This automatically turns a cam that varies the elevation an angle of the optical reflector sight to provide the required super elevation. Coincidentally, the data is fed into the range dial mounted near the sight, enabling the pilot to open and break off fire on the basis of his range readings. The pilot, for his part, keeps the target positioned in the reflector sight, computes windage as usual, and fires as often as the loader can ram the projectiles (20 in the rack and maybe more on the floor) into the breach. With Falcon constantly providing range data for the gunsight, 10 or more rounds can be fired during a single run.
C-2 Sight Head
I have seen some reference of a C-2 head in AAF correspondence but do not know anything more about it. Can anyone help?
Sight heads designed and procured directly by aircraft manufacturers.
The N-2 & N-3 series had the distinction of using a great variety of sighting heads as, besides standard government procured heads, they were also fitted with a lot of different heads designed and produced directly by aircraft manufacturers. It was indeed the custom in the early years to provide the manufacturers just with the sight and let them design/install their own sight mounts and sighting heads. Some early installations, with the gunsight fixed on the cockpit floor, did not even use any sighting head as the reflector glass was fixed on the back of the instrument or directly on the windshield (P40 B&C for example).
Most of those sight heads were also supplied with sliding sun shields and periscopic systems for over the nose vision. Note that those systems were however rarely used by pilots and usually quickly dismantled from their planes.
 All fixed gunsights of the N- series (i.e. all except the N-6 and N-8) could also be used without a reflector head. In this case the reticle was projected directly on the aircraft windscreen instead of the reflector glass.
 Source : Index of Aeronautical Equipment Vol 5 – Armament, dated March 1, 1944
 Also called bombsight head, low altitude bombsight, variable bombing reflector
 A-36, P-51A/B/C, P-39, P-40, P-47( ?), P-63, A-24 and A-25
 A-20, A-26 and B-25
 Mostly P-51B&C, but also P-39 and probably P-63 and P-40.
 Source : VMB613 website