Sir

Natasha Loder writes (Nature 407, 278; 2000) that the particular kind of four-rotor Enigma machine used by the German Abwehr — and stolen from Bletchley Park earlier this year — is very rare, and that the only other known example is owned by the US National Security Agency.

This is correct. But, rare though the Abwehr versions are, there are several other four-rotor Enigma machines in existence and available to collectors by legal means. I myself own one: No. 877, bought at Sotheby's in March 1994 (it was previously sold at Phillips in April 1993). At least three others were sold at Phillips and Sotheby's during the 1990s.