The internal units of the GRS searchlight signals are very similar to the US&S units.  See The H Internal Unit and The H-2 Internal Unit.  In the compound lens style, the internal unit contains the inner doublet lens.  Light passing through the inner doublet is then focused by the outer doublet lens contained in the signal housing to obtain the final beam.  In the stepped lens design, there is no inner doublet and the light is focused into the final beam only by the outer stepped lens.

Above.  View showing roundels and elliptical reflector which holds the bulb.

Above.  Integral power resistor.  The value of the resistor is adjusted by moving the spring-loaded slide from top to bottom along the rail.

Above.  The internal unit for use in the stepped lens style of searchlight signal has a clear flat cover and no inner doublet lens.  The internal unit for the compound lens style signal would have a curved inner doublet lens in place of this clear flat cover glass.  Other unique features common to both the stepped lens and compound lens style units include a T shaped handle on top which fits into a slide on the inside top of the signal housing, a positioning pin on each side in the top rear and a spring loaded locking cam on each side in the middle rear.

Above.  The motor which controls the signal aspect, is connected in the rear of the unit through the two middle contacts on the bottom row.  Power to the light is connected through the inside terminals on the upper row.  The voltage driving the light can be adjusted by the integral adjustable resistor.

Left.  Internal view of stepped lens housing showing the back of the lens and the top T slide, indexing hole for one of the indexing pins and catch pin for one of the spring loaded locking cams.

Above.  View of the spring loaded locking cam..  When the unit is inserted in the housing, each cam rises when it contacts its respective catch pin and then falls behind the catch pin causing the curved rear part of the cam to rest against the catch pin.  This securely locks the unit in place.  No bolts or screws are used to hold the internal unit in the housing.

To remove the unit, you must raise the cam on each side and slide the unit backward until the top T slide is disengaged.