Editing Ultra (cryptography) (section)

===Radio and cryptography===
The communications system was founded by Brigadier Sir [[Richard Gambier-Parry]], who from 1938 to 1946 was head of MI6 Section VIII, based at [[Whaddon Hall]] in [[Buckinghamshire]], UK.{{sfn|Pidgeon|2003}} Ultra summaries from Bletchley Park were sent over landline to the Section VIII radio transmitter at Windy Ridge. From there they were transmitted to the destination SLUs.

The communications element of each SLU was called a "Special Communications Unit" or SCU. Radio transmitters were constructed at Whaddon Hall workshops, while receivers were the [[National HRO]], made in the USA. The SCUs were highly mobile and the first such units used civilian [[Packard]] cars. The following SCUs are listed:{{sfn|Pidgeon|2003}} SCU1 (Whaddon Hall), SCU2 (France before 1940, India), SCU3 (RSS Hanslope Park), SCU5, SCU6 (possibly Algiers and Italy), SCU7 (training unit in the UK), SCU8 (Europe after D-day), SCU9 (Europe after D-day), SCU11 (Palestine and India), SCU12 (India), SCU13 and SCU14.{{efn|In addition, there were SCU3 and SCU4, which supported ''Y Service'' radio intercepting and direction finding facilities. These units were formed from assets of the former [[MI8|Radio Security Service]], after it was reassigned to MI6 and they were not involved in Ultra dissemination.}}

The cryptographic element of each SLU was supplied by the RAF and was based on the [[Typex|TYPEX]] cryptographic machine and [[one-time pad]] systems.

RN Ultra messages from the OIC to ships at sea were necessarily transmitted over normal naval radio circuits and were protected by one-time pad encryption.{{sfn|Beesly|1977|p=142}}