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.