Complex sentence: The first EF-10B lost in Vietnam was to a SA-2 SAM on 18 March 1966, while four more EF-10Bs were lost in Vietnam to accidents and unknown causes.
Split into simpler sentences: The first EF-10B lost in Vietnam was to a SA-2 SAM on 18 March 1966. Four more EF-10Bs would be lost in Vietnam to accidents and unknown causes.