Armored Medical Research Laboratory Fort Krstox, Kentucky INDEXED PROJECT NO. 6 - VISION IN TANKS Third Partial Report On S^^ffS^eSt No. 6-4, Study of Means for Improving Sighting Telescopes LATERAL-OFFSET SIGHT Project No. 6-4 27 September 1943 LatF/sal. Orrser S/c/^r -4evfo&ev /4ew/CAb Fsifcch /.ABiz/EAro^r' A/aj. ffZACZfrr 9, /9F3 fr/G. / 5/e,hT h/louNTFo /fl FAHtS Scale - Falf S/ze fra 4 O^t/cal TeA/AJ Scale- Full S/zE Fg. /b Ho/Zf ZObf ZA L. Ssc T/O/V F/g. Za S/oe //etv F/c. 2 c Fcoc/r V/£w P-44 F/g. 4 fk^r //£^ GA B/GHT /AySTALLAT/OK/ Fig. J Flsv'at/oh Or l/ty^AQS /a/gtal^at/ga/ / LaTTBAL O^SST S/G^r / Ag/^aeev AJmaAC iAtroCAT^^'/' Waj, Sc^r. <F &Af5 S^cf-A-^ S.,^ Fig. >5 SBcr/oA/ ARMORED MEDICAL RESEARCH LABORATORY Fort Knox, Kentucky 413 o 74-1 GNOML 27 September 1943 LATERAL-OFFSET SIGHT 1° PROJECT: Noo 6 - Vision in Tanks; Third Partial Report on Sub- project NOo 6-4 - Study of Means for Improving Sighting Telescopes0 aQ Authority: Letter Commanding General, Headquarters Armored Force, Fort Knox, Kentucky, File 400o112/6 GNOHD, dated September 24, 1942O b0 Purpose; To provide a sight especially suitable for guns of 76 mm bore and larger, and also for low velocity weapons0 2c DISCUSSION: 7 a0 For guns larger than the 75 ram, the gun trunnions are of necessity placed so far from the center of the turret ring (36" or more) that a coaxial telescope becomes unduly longo There is need for a sight which presents little travel of the eyepieceo* The proposed lateral-offset sight offers this special advantageo bo Low velocity weapons such as howitzers and mortars which require an angle of elevation greater than that which can be accommodated by range marks in the reticule, require a special handling of the direct-laying sight allowing the whole sight to be accurately moved in elevation with respect to the guno The lateral-offset sight especially lends itself to this useo ✓ co Guns larger than the 75 mm produce such excessive smoke and blast that a considerable time elapses after firing before satisfactory vision of tracer can be established from vantage points near the gun0 Since the lateral- offset sight pierces the side armor its line of vision is removed from the gun by almost a yard, thus offering as great as possible freedom from blast dis- turbances o While some correction must be made for parallax either in the reti- cule or by allowance in laying the gun, this does not present a serious objectiono do The optical properties of the lateral-offset sight are similar to those of a wide field 6 power monocular (half of a binocular) and identical to the 6-power system of the T-8 Dual Sight; namely, Power 6x; True Field 11° 20'; Exit Pupil 7 mm; high transmission and low veiling haze. * See Armored Medical Research Laboratory Report: Placement and Mounting of Sights in Tanks. Project Noa 6-2, 6-4, 9 June 1943° 1 This type of optical system is capable of the finest properties obtainable and is far superior in its potentialities to the coaxial straight telescope0 (Any power from 2x to 8x is feasible in the lateral-offset sight without drastic changes in layout.) e. The lateral-offset sight lends itself to the employment of a long lever parallelogram linkage. This long lever linkage provides a mechan- ical advantage four times greater than that used in the periscope and eliminates the fundamental objection to linkage; namely, inaccuracy of alignment unless the highest precision bearings and structure are used. f. The method of mounting and linking of the lateral-offset sight are illustrated in the appended drawing. 3o CONCLUSIONS: ae A lateral-offset sight is suitable for use with guns larger than the ?5 mm (as mounted in turrets of the present ring diameter) where it is necessary to avoid the excessive eyepiece excursion of the coaxial sight which occurs with elevation of the guru b. The lateral-offset sight reduces to some extent the interference arising from smoke and blast. co The lateral-offset sight provides optimum optical properties. do The lateral-offset sight meets the need for elevation in excess of those possible in a fixed reticule sight. 4. RECO^CENDATIONS: a0 That the lateral-offset sight be considered for use in all turrets, that mount guns in excess of 76 mmo* b. That the lateral-offset sight be considered for use wherever direct laying requires elevations relative to the gun in excess of 3 degrees, i.e., with low velocity howitzers, etco Reported by: Frederick S. Brackett, Major, Sn C APPROVED WILLaRD MACHLE Colonel, ?Aedical Corps Commanding * Owing to the advanced state of development of the M4 tank mounting the 76 mm gun, a change from the coaxial to the lateral-offset sight is not proposed for this vehicle. For all future tanks mounting the ?6 mm gun, however, the lateral- offset sight is recommended. 2 appendix Io The accompanying drawings illustrate the mechanical requirements for placement, mounting and linking of the lateral-offset sight. 2. The lateral-offset sight pierces the side armor at approximately eye level as shown in Figure l0 Its mounting is as follows: a. It is supported by two ball races, one rigidly affixed to the sidewall of the armor by means of a sleeve pressed into the aperture. The other supported from the roof of the turret by a pillow block. These ball races are partially self-aligning and of precision quality., The pillow block is provided with a centering adjustment to obtain parallelism between the axis of the sight and the axis of the gun trunnions. bo A long lever linkage is laid close to the recoil mechanism, thereby avoiding interferences with the gunner. c. The linkage connecting rod is anchored to the gun cradle either by a bolted and pinned block or by means of a cast ear on the elevation sector0 d. Figure 1 shows the general arrangement of the mounting and the placement of the sight relative to the periscope when viewed looking forward from the gunner's position. Only one difficulty arises in the mounting; namely, that in the existing tank models the elevation hand wheel is too close to the recoil mechanism to allow the introduction of the linkage with- out danger of barking the knuckles. A slight change in the design of the elevation mechanism avoids this difficulty0 e. Figure 2 shows the layout of the optics. This is identical with the six power optical train of the T-8 Dual Sight, with the exception of the outside prism which is 2" long instead of 7"o Production parts will be inter- changeable. f. Figure 3 shows the linkage arrangement when viewed laterally along the axis of sight or gun trunnions. go Figure 4 shows a full scale view of the sight and side armor perforation as seen from the gunner's position. The-necessary modification in shape of the sidewall together with a protective shield is illustrated. h. Figure 5 shows a horizontal section through the sight and pillow block. This figure also shows the horizontal section of the armor perforation with the necessary modification in shape. i. Boresighting is accomplished very simply - (1) In elevation, by a tangent screw and clamp attached to the linkage lever as shown in Figure 3 and 5= (2) In azimuth or lead by a lateral motion of the reticule. 1 jo Elevation adjustment for low velocity weapons can be easily accomplished by calibrating the tangent screw head, (indicated in i(l) above)o 2