On March 31, 2015 at 16:47:56 MSK (13:47:56 UTC) the Space Forces conducted a successful launch of a Rockot space launcher with Briz-KM booster stage from the launch pad No. 3 of the launch complex No. 133 of the Plesetsk test site. The launcher delivered into orbit three Gonets-M communication satellites (21L, 22L, and 23L) and a small satellite designated as Cosmos-2504.
According to the designer of the system, the Information Satellite Systems, this launch completes the deployment of the Gonets-D1M communication system, which now includes 12 satellites. Previous Gonets-M launch took place in July 2014. Russia alos operates a military counterpart of the Gonets system, known as Strela (or Rodnik). The most recent launch of this program took place in May 2014.
The Gonets satellites have been assigned NORAD catalog numbers 40552, 40553, and 40554, their international designations are 2015-020A, 2015-020B, and 2015-020C.
The Cosmos-2504 satellite, launched along with the Gonets-Ms, is believed to be a small maneuvering satellite similar to Cosmos-2499, which was also a supplementary payload in the May 2014 launch. It appears that its the object 2015-020D/40555.