There is no location called 'Shanwick'. This name is made from the first part of the transmitter site, 'Shannon' (where the wellknown Volmet is), and from the second part of 'Prestwick', where the control center is. So actually, as transmitting from Ireland, it is an Irish utility station...
very chaotic traffic on 8879
kHz: both the North Atlantic and the Africa / Indian Ocean World
Major Air Route Area's (WMARA) booming in, revealing Gander,
Shanwick, and Iceland
from the one, and Beira,
Lilongwe, and Antananarivo
from the other side (rb, 1985)
a QSL letter from 1983...
...and the frequency listings from 1983
a verification of a Concorde-flight (Michael Oexner, 1990)
here is the homepage of the Service
------------------------------------------------------------
Frequencies Voice:
2872
2899
2962
2971
3016
3023
3476
4675
4715
5598
5616
5649
5680
5718
6622
8825
8831
8864
8879
8891
8906
8945
11279
11336
13291
13306
17946
Frequencies Radioteletype:
5028
5718
7716.6
8843
11384
Systems used:
HF-ACARS
MFSK