The rotors of the KL-7 resemble those of the famous German Enigma machine and other wheel-based cipher machines. Each rotor has a series of flat-faced contacts on the right side, and the same number of spring-loaded contacts on the left. It also has an adjustable index ring with the letters of the alphabet on it, and an inner core which connects the contacts on one side with the contacts on the other side. There are some significant differences with the Enigma however.





First of all, a KL-7 rotor has 36 contacts, whereas an Enigma wheel has 26 contacts. Of the 36 contacts, 26 are used for the encryption of the 26 letters of the alphabet. The remaining 10 contacts are looped back to the input (see below). This results in a re-encipherment of part of the text, which is covered in US Patent 2,984,700 filed by Albert W. Small on 22 September 1944.



Each wheel has an index ring with 36 positions, each separated by a narrow gap. Only 26 positions are identified with one of the letters of the alphabet. The rest is empty. When unfolded, the index ring looks like this:





Another important difference, is the omission of the reflector (Umkehrwalze). In encoding mode, one side of the rotor basket is the input and the other side is the output. In decoding mode, all contacts are swapped, so that the output becomes input and vice versa. This has the advantage that, unlike on Enigma, a letter can become itself on a KL-7. Swapping all contacts however, does involve a rather complex multi-contact switch, which is integrated with the KL-7 keyboard.





The Drum or Rotor Basket of the KL-7 consists of a metal cage with 8 wheels on a spindle (KLK-7). The forth wheel from the left is fixed in position. It never rotates and hence does not have a window to show its setting. This wheel is sometimes referred to as the NSA rotor. For each of the other 7 wheels, a window is present in the cage. Through this window, three successive letters of the wheel are visible. The topmost letter visible through the window, represents the current setting. This position is indicated by a white line from left to right.





Each KL-7 machine was supplied with 12 rotors, marked A-L, in a metal box. The L-rotor was the so-called stationary NSA wheel, that was used in position 4. Of the remaining 11 rotors (A-K), 7 would be placed in the rotor basket on a given day, in a particular order, as per cipher instructions (codebook).





The user would remove the rotor basket from the machine by releasing two levers; one at either side of the basket. Once removed, the rightmost end-plate of the basket can be removed by releasing a pawl that locks it on the spindle. After removing the rightmost end-plate, the rotors can be taken from the spindle. The spindle itself stays in the basket at it is fixed to the leftmost end-plate, that in turn is fixed to the cylindrical basket (see image above).