Editing Special Operations Executive (section)

==Communications==

===Radio===
[[File:Kofferset 3MK II.jpg|thumb|B MK II receiver and transmitter (also known as the B2 radio set)]]

Most of the resistance networks which SOE formed or liaised with were controlled by radio directly from Britain or one of SOE's subsidiary headquarters. All resistance circuits contained at least one wireless operator, and all drops or landings were arranged by radio, except for some early exploratory missions sent "blind" into enemy-occupied territory. SOE wireless operators were also known as "The Pianists".<ref>{{cite web|url=http://www.campx.ca/georgesbegue.html|website=campx.ca|access-date=20 April 2018|last=Brisson|first=Richard|title=Georges Bégué, MC|archive-date=21 June 2023|archive-url=https://web.archive.org/web/20230621010918/http://www.campx.ca/georgesbegue.html|url-status=live}}</ref>{{Better source needed|date=April 2018}}

At first, SOE's radio traffic went through the SIS-controlled radio station at [[Bletchley Park]]. From 1 June 1942, SOE used its own transmitting and receiving stations at [[Grendon Underwood]] in [[Buckinghamshire]] and [[Poundon]] nearby, as the location and topography were suitable. Teleprinters linked the radio stations with SOE's HQ in Baker Street.{{Sfn|Foot|1999|pp=109–110}} Operators in the Balkans worked to radio stations in Cairo.{{Sfn|Foot|1999|p=108}}

SOE was highly dependent upon the security of radio transmissions, involving three factors: the physical qualities and capabilities of the radio sets, the security of the transmission procedures and the provision of proper [[cipher]]s.

SOE's first radios were supplied by SIS. They were large and clumsy, and required large amounts of power. SOE acquired a few, much more suitable, sets from the Poles in exile, but eventually designed and manufactured their own, such as the [[Paraset]], under the direction of Lieutenant Colonel F. W. Nicholls of the [[Royal Corps of Signals]], who had served with Gubbins between the wars.{{Sfn|Wilkinson |Astley |2010 |pp=29, 115}}{{Sfn|Foot|2004|pp=109–110}} The A Mk III, with its batteries and accessories, weighed only {{convert|9|lb|kg}}, and could fit into a small [[attache case]], although the B Mk II, otherwise known as the B2, which weighed {{convert|32|lb|kg}}, was required to work over ranges greater than about {{convert|500|mi|km}}.{{Sfn|Foot|1999|pp=108–111}}

Operating procedures were insecure at first. Operators were forced to transmit verbose messages on fixed frequencies and at fixed times and intervals. This allowed German [[direction finding]] teams time to triangulate their positions. After several operators were captured or killed, procedures were made more flexible and secure.{{Sfn|Foot|1999|p=106}}

As with their first radio sets, SOE's first ciphers were inherited from SIS. [[Leo Marks]], SOE's chief [[cryptographer]], was responsible for the development of better codes to replace the insecure [[poem code]]s. Eventually, SOE settled on single use ciphers, printed on silk. Unlike paper, which would be given away by rustling, silk would not be detected by a casual search if it was concealed in the lining of clothing.

===BBC===
The [[British Broadcasting Corporation|BBC]] also played its part in communications with agents or groups in the field. During the war, it broadcast to almost all Axis-occupied countries, and was avidly listened to, even at risk of arrest. The BBC included various "personal messages" in its broadcasts, which could include lines of poetry or apparently nonsensical items. They could be used to announce the safe arrival of an agent or message in London for example, or could be instructions to carry out operations on a given date.{{Sfn|Foot|1999|pp=99, 142–143}} They were used, for example, to mobilise the resistance groups in the hours before [[Operation Overlord]].

===Other methods===
In the field, agents could sometimes make use of the postal services, though these were slow, not always reliable and letters were almost certain to be opened and read by the Axis security services. In training, agents were taught to use a variety of easily available substances to make invisible ink, though most of these could be detected by a cursory examination, or to hide coded messages in apparently innocent letters. The telephone services were even more certain to be intercepted and listened to by the enemy, and could be used only with great care.

The most secure method of communication in the field was by courier. In the earlier part of the war, most women sent as agents in the field were employed as couriers, on the assumption that they would be less likely to be suspected of illicit activities.{{Sfn|Foot|1999|p=160}}