Submarine Periscope Design
The following pages deal mainly with submarine periscope optical design. While the sub periscope possesses unique characteristics overall, its optical design is very repreentative of a much broader class of periscope-like instruments such as armored vehicle sights. These are addressed elsewhere on this site.
The periscope optics share the space in the periscope head and tube with a mix of antennas, transmission lines, mechanical actuators, motors, electronic transducers, sensors and related components.
In a typical sub periscope, the space envelope for the mast optics typically measures about 45 feet in length and about 4 inches in diameter. The periscope has three basic sections. At the top there is the head and neck, which in some designs is thin, long and tapered; next, there is the long cyiindrical mast; and, lastly, the Eyepiece Box which is attached to the mast at the lower end. In advanced electro-optical periscopes, the Eyepiece Box is replaced by a Display and Control unit which houses electronic sensors and displays.
The head optics consist of a window and right angle prism. The prism can be rotated about an axis by the operator to slew the line of sight in elevation. The line of sight can be directed to look downward 15 degrees or to look in any direction from 0 degrees at the horizon to points near the zenith.
The line of sight is directed in azimuth by operator rotation of the entire periscope in its bearings using the training handles attached to the Eyepiece Box.
The operator changes line of sight direction in elevation by rotation of the left training handle and selects magnification by rotation of the right training handle. Detents in the rotation mechanism are provided to produce either 1 1/2 x or 6 x magnification. A higher 12x magnification exists in the more recent periscope designs.
A removable eyepiece assembly is attached to the Eyepiece Box. A staunching window mounted in the Eyepiece Box directly in front of the eyepiece provides a safety barrier in the event of a flooded periscope. A focus control knob is provided on the Eyepiece Box near the right training handle.
Periscope System Design Considerations
The periscope operates in harsh saltwater environments from the arctic to the tropics. It also must withstand great pressures at ocean depths. Head window design must provide for de-icing and de-misting means while not impairing the required viewing capability.
The window must be thick and strong enough to avoid fracture under high pressure yet large enough in area to achieve the required optics aperture size, field of view and field of regard in slewing the line of sight in elevation.
The interior space of the periscope is filled with pressurized dry nitrogen to prevent condensation on the optics. The reticle must be kept free of dust particles to avoid “false alarms” at sea. Sufficient radial clearance between the mast optics and the inner wall of the periscope tube must be provided for passage of mechanical control rods, waveguides, and other electrical runs which travel from top to bottom of the tube.
A thick glass staunching window is provided at the lower end of the mast to keep ocean water from entering the sub in the event of a broken or damaged periscope head or mast. Specially designed, “subsafe”, hermetically sealed connectors linking the mast electrical runs to the sub interior are provided for the same reason.
The more recent periscopes replace mechanical drives with electrical drives for optics magnification change mechanisms and head prism line of sight control and stabilization. Heat generation by these devices can impact optical performance. Design measures must be taken to mitigate or eliminate thermal effects.
Thus, in the optical design of the periscope, the optical designer must interact with other periscope engineers in the other disciplines, including mechanical, thermal, structural, electrical and microwave.
This simple, very brief overview on sub periscope design is intended to serve as a backdrop for the discussion of periscope optical design which appears in the following pages.
The photographs on this page have been contributed by Mr. H. Torberg, a long time Kollmorgen engineer and photographer. Some retouching and annotation has been added by the author.