Hagelin C-48A (A present from Michael Müller, M.)

is a portable mechanical device to cypher / decypher tactical messages.
 
In the early 40s the Swedish inventor Hagelin developed it; it was issued 1943 and was built in Sweden
It was used in the USA as M-209; The picture gallery shows a comparison between M-209 and C-48. M-209 uses one paper tape for cyphered and decyphered text wheras C-48 uses two paper tapes, one for the cyphered and one for the decyphered text.
 
The C-446A later was developed from the M-209, was built by CRYPTOTEKNIK in Sweden and again uses two paper tapes. There also are two locks in both C-446A and C-48 for the outer and the inner housing, using the same key. (M-209 has no lock)
 
It looks that by developing the C-446A the C-48 was re-envented.
 
Cypering:
The letters to cypher are chosen on a dial and cypered by turning a handcrank. Space is replaced by the letter "Z" The cyphered result is printed out in five- letter groups on a paper tape and may be forwarded by Morse code.
 
Decyphering:
After turning a knob from "C" (cypher) to "D" (decypher) the letters received are chosen on the dial, and by turning the hand crank the deciphered text is printed out on the second paper tape.
 
The algorithm used is rather simple (it repeats itself after the ca 101 millionth time). Decyphering by the enemy took only a short time, so this machine was used for messages that were no longer important after some hours.