SAVILLE is a classified NSA Type 1 encryption algorithm, developed in the late 1960s, jointly by the Government Communications Headquarters (GCHQ) in the UK and the National Security Agency (NSA) in the US.
Little is known publicly about the algorithm itself due to its classified nature and inclusion in the NSA's Suite A.
Some documentation related to the KYK-13 fill device and statements made by military officials confirm that SAVILLE has a 128-bit key, which consists of 120 key bits and an 8-bit checksum.
[1] On the AIM microchip, it runs at 4% of the clock rate (compare DES at 76% and BATON at 129%).
The Cypris chip mentions two modes; specifications for Windster and Indictor specify that they provide Saville I.