The primary differences between the “H” and “H-2” searchlight signal styles relate to the design and placement of the lenses.  All searchlight signals have a compound lens design.  The internal unit contains the first lens, and the outer case holds the second lens.  These are commonly referred to as the "inner doublet" and the “outer doublet" lenses.

US&S manufactured two primary styles of searchlight signals.  The first, and earliest, is know as a style “H” signal. The “H” stood for “Hall", as in Thomas Hall, the inventor of the searchlight signal.  His company, the Hall Signal company, was acquired by US&S in 1925.  This signal has a concentric prism outer doublet front lens with an integrated center hot spot deflecting prism.  This type of outer doublet lens is still used in modern color light signals today.

The second primary style of US&S searchlight signal is known as style “H-2”.  In the H-2 signal, both surfaces of the outer doublet lens are smooth and contains no prism surfaces.  To create a deflecting beam for close-up viewing, the style H-2 signal has a small deflecting prism located between the inner and outer doublet lenses.  To accommodate this deflecting prism, the style H-2 signal has an extension on the front of its signal housing. This also allows the deflecting prism to be adjusted through a small hatch on the top of the extension.  Consequently, the style H-2 signal is about five inches longer than the style H signal. Also, when mounting targets or backgrounds on an H-2 signal, extensions must be used to move the target forward to the same plain as the outer doublet lens. The H-2 is by far my favorite railroad signal.

US&S manufactured additional signals styles based on the H-2.  These are identified as styles H-3 and H-4 and differed only in the design of the hinged back door.  They each have a protruding section on the lower part of the back door to allow more room for complicated signal connections.  See the H-5 Style description for an example of a protruding back door.

Above.  Inspection/adjustment hole in H-2 extension case.  The close-up prism is visible through the hole.

Above.  Drawing of style “H” signal.  This signal uses a standard stepped outer doublet lens which usually contains an integral close-up or deflecting prism in the center part or bulls eye of the lens.

Above.  Drawing of style “H-2” signal.  This signal uses a smooth surface outer doublet lens.  The close-up prism is located between the inner and outer doublet lenses.

Below.  Side views of the style H and H-2 ground mounted signals which show the added length of the H-2 case extension.  The comparison is a bit difficult because the H signal in the photo on the left also has a phankill unit mounted in front of the outer doublet lens under the visor.