Cool looking cover - Unfortunately the band doesn't quite match it.  Although listed by several sources as NWOBHM, I would consider them more Hard Rock/Prog (There's even flute a la Jethro Tull).  Formed in 1978 by bass/lead vocalist Gordon Rowley, who came from progressive rock band Strife  (Nightwing originally was named Gordon and Friends). There is a rumor floating around that Rowley declined joining Rainbow in order to form this group.