Technical Informations
Appearance and dimensions
M-138
- The base is a flat aluminium board which measures 16″ x 11″ (40.64cm x 27.94cm).
- Cylindrical rods, 1/8″ (3.2mm) in diameter, separate the board in 25 horizontal channels.
- The rods are spaced 5/8″(1.6cm) apart and are fixed with 4 rivets each. Every fifth is black, starting with the topmost rod.
- A ruler, attached to a rod fixed at the bottom edge, slides from side to side.
- Two bars are fixed on the left and right edge, atop the rods so the paper strips can slide under.
- The back side features rubber feet, and a support so the device can stand at a 45° inclination.
M-138 cipher device – National Cryptologic Museum
M-138 cipher device (back) – National Cryptologic Museum
M-138-A
- The device has an hinged aluminium base, 14 5/8″ x 15 11/16″ (37.14cm x 39.84cm) unfolded, weighing about 2kg.
- The base has 30 milled channels.
- “CLEAR TEXT” is written above the first and last (53rd) columns, and “DO NOT COPY” above the center (27th) column
- A vertical line appears above and below each odd column, and a dot above and below even columns.
- An hinged ruler can slide along a groove at the bottom of the base. It is 1/2″ wide and removable.
M-138-A device – National Cryptologic Museum
M-138-A device, closed – National Cryptologic Museum