German AA Pivoted Ring Sight, WWII Tactical and Technical Trends, No. 41, December 30, 1943 (Lone Sentry)

A translation of a document published by the Flak Inspectorate of the German Air Ministry, dated April 1943, gives some interesting details pertaining to the German AA pivoted ring sight Schwebekreisvisier 30/38. It is a one-man sight and needs no personnel other than the layer for the current feeding in of the estimated range, course, etc. It is used for "firing with AA sight without rangefinder" with the 20-mm single-barrelled weapon and as an auxiliary sight with the 20-mm four-barrelled weapon. The pivoted ring sight has been produced as the Schwebekreisvisier 30 for the 20-mm Flak 30 and as the Schwebekreisvisier 38 for the 20-mm Flak 38.

a. Description

The pivoted ring sight consists of the following main parts: the body, the guideway for the slide, the mounting for the eyepiece, the attachment to the circular foresight, the device for adjusting according to speed, and the bracket for the telescopic ground sight.

(1) The body connects the sight on the pivoted bracket arm with the guideway and varies according to the mark of sight. The purpose of the eye rest is to center the eye and to protect it during firing. To this end it contains an aperture backsight and an eyepiece. The slide with the attached forward sight serves as a holder for the pivoted ring and moves up and down the guideway. The foresight is fastened to the slide by a clamping lever. In this the pivoted ring is placed so as to allow it to rotate. The angle at which the pivoted ring is set can be altered by means of the pendulum; when the latter is clamped in a horizontal position, the ring is vertical. This is the travelling position. Each sight is provided with two sets of pivoted rings and each set allows for three different ranges of speed. The foresight bead is fixed in the middle of the axis of the pivoted ring.

(2) The device for adjusting according to target speed consists of an adjusting knob, an adjusting pointer on the slide, and a rotatable drum which is provided with scales for three ranges of speed. The three pivoted rings are designed in different sizes and allow for a range of 1,200 meters (1,320 yards) at the following ranges of speed:

Small ring:       50-75 meters per second (120-180 mph)
Medium ring:      75-115 meters per second (180-280 mph)
Large ring:       115-180 meters per second (280-420 mph)

(3) The intermediate values can be interpolated on the corresponding scales of the drum. The pivoted ring can be positioned eccentrically along the axis of the foresight to allow for variations of TE in accordance with different angles of sight.

(4) The bracket of the telescopic sight is only issued with the 38 model and is fastened on the body of the sight.

(5) The principle of the sight. By means of the pendulum the pivoted ring is always kept parallel to the plane of flight. On the outer edge of the ring is the present position and in the middle of the ring -- the bead of the foresight -- is the future position. The line of sight runs from the layer's eye through the aperture rearsight and the outer edge of the pivoted ring to the target; the line of fire goes from the layer's eye through the aperture rearsight and the bead of the foresight to the future position of the target.

b. Method of Operation

As stated above, the pivoted ring sight is used for "firing with AA sight without rangefinder" (formerly called "firing by observation of tracer"). When laying through the pivoted ring, fire is opened at a maximum range of 1,320 yards, which is the limit of effective fire. The section commander observes the position of the bursts and orders that different deflections, if any, are to be set in. The pivoted ring sight is not used for the engagement of ground targets. For these targets the telescopic ground sight is used; if this has not been issued the gun will be laid through the rear and foresight of the pivoted ring sight.

(1) For good laying with the pivoted ring it is essential that the layer be seated correctly so that at angles of sight from about 10° to 60° his eye can rest comfortably on the eyeshield.

(2) It is the responsibility of the troop commander from his experience of the normal speeds encountered in his particular area to order which of the three pivoted rings is to be fitted into the sight. The speed scale appropriate to the ring chosen must then be inserted in the drum. It is essential that the correct speed scale be set in, since during the engagement no alteration of this scale can take place.

(3) To lay on the target the layer presses his eye to the eyepiece, through which the aperture rearsight will appear only as a hazy circle. This rearsight must exactly cover the foresight. By operating the traversing gear he displaces the bead of the foresight in the apparent line of flight of the target to a point so far in front of the target that the nose of the target cuts the rim of the pivoted ring, which appears at this moment to be an ellipse. The amount of tracking-off and the sighting of the target along the rim of the ring must be so chosen that the target always seems to be flying from that position towards the foresight bead. If in the case of a surprise attack there is no time to align the target exactly with the pivoted ring the layer must at least keep the foresight bead in front of the target and in the apparent line of flight.

(4) Fire is opened on the order of the section commander after the gun has been laid on the target by means of the pivoted ring. After fire has been opened the layer opens his other eye and continues firing after observing his bursts. Even in this case the pivoted ring acts as a guide for the deflections to be set in.

(5) At angles approaching 0° the pivoted ring appears to be a line and the bead to be a thickening of this line. In this case the line of flight is sighted along the lower edge of the line. The lateral deflection must be estimated and the following is a guide for this estimation:

Complete fuselage visible: aiming point on the outer edge of the pivoted ring (maximum deflection);

Half fuselage visible; half the above deflection;

Fuselage invisible (direct approacher or receder); aiming point through the bead.

(6) With changes of height, sighting takes place exactly as described in paragraphs (3), (4) and (5), except that with diving approachers the bead becomes the aiming mark instead of the pivoted ring.