Further details are now available on the operation of the special night-driving
equipment with which German military vehicles are equipped and which was briefly
described in Tactical and
Technical Trends, No. 1, p. 21. It is
believed that the equipment is sufficiently ingenious in its design to
warrant a complete study at this time.
The equipment consists of the following parts:
(a) The blackout headlight. This is mounted on the left-hand side of the
vehicle between 32 and 48 inches from the ground.
(b) The special interval-judging tail light, and stop light. This is
carried on the left-hand side of the vehicle (see accompanying sketch, Fig. 1).
(c) The additional tail light, fitted with a dimming device, and carried on
the right-hand side of the vehicle (Fig. 2).
(d) A five-stage dimmer switch on the dashboard (Fig. 3).
a. The headlight is of a peculiar flattened shape, and employs a
horizontal 35-watt lamp which gives off light to the rear against a semi-oval mirror. This
mirror in turn reflects the light back through a glass diffusion-panel under
the overhanging hood.. A soft, almost flat-topped beam of light results. The
beam is projected for a length of 30 to 40 yards and a width of about 25 yards, and
is particularly diffused toward the edges.
It is claimed that the beam from the headlight is invisible when on "low" from
heights exceeding 1,600 feet; when on "medium" above 2,600 feet; and
when on "full" above 4,800 feet. The same distances also apply to ground
b. The interval-judging tail light and stop light (Fig. 1) consists of a
panel divided into an upper and lower half. The upper half comprises the
interval-judging device itself; the lower half consists of a normal red tail light, and
a yellow stop light which functions when the brakes are applied. The half which
is not in use is obscured by a shutter which is hinged about the horizontal axis
of the panel.
The upper half of the panel, the interval-judging device, has four small
rectangular windows, grouped in two pairs, and showing a yellowish-green light.
The operation of this device is based on the limitations of the human eye, which
is capable of perceiving adjacent sources of light as actually distinct and
separate only within certain distances.
Thus, at distances greater than 35 yards, the four rectangles of light will be
perceived by the driver behind as one point of light. At about 35 yards
distance, he will see two lights, and finally, when he is 25 yards away, all four
rectangles of light will be visible.
All that is required of a driver in a column is that he keep such an interval
between him and the vehicle ahead, that two points of light are always visible. Thus a
column interval of 25 to 35 yards will be constantly maintained.
On the under-side of the housing which contains the interval-judging device is a
shutter which, when opened, allows a dim light to be shed downward on the license
c. The right-hand tail light (Fig. 2) is compulsory under the German
regulations, which require the vehicle-width to be indicated from the rear, as
well as from the front. The fixture has two windows, one above the other, the
upper one showing a dim light, the lower one a normal light. The change from
one to the other is effected by turning a rotary shutter.
d. The Apparatus in Use
The degree of light can be varied according to the proximity of the enemy, by
different switch positions. (See five-stage dashboard switch, Fig. 3.)
STAGE 0 -- All lights out.
STAGE H -- Blackout headlight out; only the interval tail light on. This is
used when driving in column if the nearness of the enemy makes it necessary
for vehicles to drive without the blackout headlight, or for the leading
vehicle only to have the light on. Cannot be detected from the air, and on
the ground not beyond 300 yards.
STAGE V 1 -- Blackout headlight giving minimum light; interval tail light
switched on. To be used on very dark nights when in the proximity of the
enemy, and always to be used when driving into artillery positions, assembly
points, etc. Cannot be detected beyond 500 yards from the air or on the
ground. On lighter nights, instead of V 1, Stage V 2 can be used
without danger, but not in the immediate neighborhood of the enemy.
STAGE V 2 -- Blackout headlight giving medium light; interval tail light
switched on. To be used near and behind the front, e.g., when
advancing to the front. Cannot be detected from the air or on
the ground beyond 800 yards.
STAGE V 3 -- Blackout headlight giving maximum light; and interval tail
light switched on. To be used during blackout exercises in peacetime, etc. Cannot
be detected from the air or on the ground beyond 1,500 yards.
Where there is no actual danger of recognition by the enemy, vehicles
can travel with the blackout headlight full on, and the rear license plate
illuminated, as well as with the two tail lights and the stop light at their
full strength. In other words, the dimming-switch will be at Stage V 3; the
hinged shutter on the interval-judging panel will be up, covering the four
windows of the interval tail light, and exposing the left-hand tail light
and stop light; the shutter underneath will be open, permitting light to
fall on the license plate; and the right-hand tail light will be set to bright.
At any sign of the enemy, it is necessary to stop the vehicle and to make
the following adjustments before proceeding:
Push down the shutter on the interval-judging panel, thus exposing the
interval-judging device. Close the shutter underneath, cutting off the
illumination to the rear license plate. Rotate the dimming disk on the
right-hand tail light.
The head light of the leading vehicle is switched down to the lowest
possible point consistent with the darkness of the night and the danger of
observation; the darker the night, the less light is used.
In convoys, only the leading vehicle will normally use its
blackout head light, and all the remaining vehicles will
switch to the H position, using the interval-judging panel
to keep position.