The Enigma Uhr
1944 · Uhr Switch · Work 451 of 1,871
A small wooden switch box painted sand beige, about the size of an alarm clock, a large round wooden knob on its face, a small rectangular window above the knob with a two-digit number printed on a white enamelled mechanical wheel turning behind the glass, the digits black and plain, a rotary switch inside with forty positions, a thick bundle of twenty textile covered cables running from its base to the plugboard of a cipher machine standing beside it, the plugs on the cables in two colours, red and black, metal brackets clamping the box to the side of the machine, both on a plain wooden table, a single work lamp from above at an angle, the beige wood and dark cables against grey shadow, the room behind in darkness.
- What it was used for
- An add-on box connected to the Enigma's plugboard. A 1945 Bletchley Park survey of German Enigma usage describes "a device called Enigma Uhr which can be attached to the Stecker board": from the single connection plugged up for the day, turning it to one of 40 positions produced 40 "mostly non-reciprocal" steckers. According to the same paper it was used on some Air Force keys, naming Jaguar as an example.
- What was new
- What was new was the break with a property every Enigma had relied on: if the plugboard swapped A with B, it also swapped B with A. The Uhr removed that reciprocity, and did so without touching the machine - a box with a rotary switch instead of a new rotor or a new procedure. The barb: the remedy largely missed the British method. Dirk Rijmenants records that the Bombe excluded the plugboard wiring from its reasoning anyway, so the Uhr had "little effect". The 1945 Bletchley paper is more precise: the D-methods "are unaffected, since they do not assume Stecker reciprocity", but "for a bombe run with known reflector, the diagonal board must be dispensed with".
Connections
Every connection names its kind. “Forerunner” on its own would be a claim.
- Works withEnigma I with Plugboard1932Clamped to the right-hand side of an Enigma I, the Uhr replaced the ten plugboard cables with 20 plugs. A 40-position rotary switch turned the day's stecker into 40 mostly non-reciprocal ones; at position 00 it behaved like ordinary cables.Source: Enigma Uhr (Crypto Museum) · Tentative List of Enigma and Other Machine Usages, 30 March 1945