|Known counterpart stations|
M13a was a variant of M13, where the intro was ID ID ID 000, rather than just the ID.The format was otherwise identical.
It was used on one schedule - 2nd and 4th Monday and Tuesday of each month at 21:00 UTC. ID changed monthly.
- ENIGMA Control List, Revision #25, p. 17 [accessed October 7th, 2014]