STINGRAY radio check with Croughton Airways on 6750, now going to the discrete frequency 9017 for RTTY traffic.
Later called and advised going to 'F315' and will monitor 'P lower'.
USAF tactical callsign, working Croughton Airways.
The reference to 'F315' refers to a designated 'Mystic Star' VIP HF frequency, the assignments of which are frequently changed. This is part of the 'Giant Talk' USAF global HF communications system
VVV MG3K BRAVO 08:29 F290, 38.30n 06w 09:15, 38.30n 15w 10:xx
U S Navy, P-3 (working Lajes Airways on 6750)
RETRO 61 39n 20w 17:06 F210 38n 15w 17:32, 38n 09.13w next
USAF, fighter, from Lajes on an eastbound oceanic transit (working Lajes Airways)
[Monitored the previous day inbound to Lajes, via KILO (38.28n 30.22w) F250, 38.31n 28.41w 23:57, GS next]