Operation Valkyrie
The author later published a number of further spin-off 633 squadron novels between 1975 and 1996, and one more in 2007. Those books are: "Operation Rhine Maiden" (1975); "Operation Crucible" (1977); "Operation Valkyrie" (1978); "Operation Cobra" (1993); "Operation Titan" (1994); "Operation Crisis" (1995); "Operation Thor" (1995); "Operation Defiant" (1996); and "Operation Safeguard" (2007).