  Three Galactic O-type stars belong to the rare class of Of?p objects: HD108,
HD191612, and HD148937. The first two stars show a wealth of phenomena,
including magnetic fields and strong X-ray emission, light variability, and
dramatic periodic spectral variability. We present here the first detailed
optical and X-ray study of the third Galactic Of?p star, HD148937.
Spectroscopic monitoring has revealed low-level variability in the Balmer and
HeII4686 lines, but constancy at HeI and CIII4650. The Ha line exhibits profile
variations at a possible periodicity of ~7d. Model atmosphere fits yield
T_{eff}=41000+-2000K, log(g)=4.0+-0.1, Mdot_{sph}<~ 10^{-7}Msol/yr and a
surabondance of nitrogen by a factor of four. At X-ray wavelengths, HD148937
resembles HD108 and HD191612 in having a thermal spectrum dominated by a
relatively cool component (kT=0.2keV), broad lines (>1700km/s), and an
order-of-magnitude overluminosity compared to normal O stars (log
[L_X^unabs/L_BOL] ~ -6).
