Answer:

UBOAT

AnswerCrossword Clue
UBOATAttacker of allied ships
UBOATAxis predator
UBOATWWI menace
UBOATGerman sub
UBOATGerman submarine
UBOATPeriscope's source
UBOATRed October's ancestor
UBOATConvoy raider
UBOATGerman WWII sub
UBOATSub
UBOATWolf-pack member
UBOATWWII sub
UBOATNaval vessel during WWII
UBOATVessel scuttled during Operation Deadlight
UBOATDestroyer's foe
UBOATWWII vessel
UBOATWWII submarine
UBOATMenace to Allied ships
UBOATWWII naval menace
UBOATHamburger's sub?
UBOAT"Lusitania" sinker
UBOATGerman war sub
UBOATWWII sea menace
UBOATWWII sea threat
UBOATWolf pack ship
UBOATGer. submarine
UBOATSinker of liners
UBOATWolfpack member
UBOATWWII torpedo launcher
UBOATWolf pack member
UBOATLusitania sinker
UBOATWW II sub
UBOATWWII German threat
UBOATWWII menace
UBOATWWII threat
UBOATWWII attacker
UBOATWWII predator
UBOAT"Das Boot" setting
UBOATWWII German sub
UBOAT"The Enemy Below" threat