  We undertake an optical and ultraviolet spectroscopic analysis of a sample of
20 Galactic B0 - B5 supergiants of luminosity classes Ia, Ib, Iab and II.
Fundamental stellar parameters are obtained from optical diagnostics and a
critical comparison of the model predictions to observed UV spectral features
is made. These parameters are derived for individual stars using CMFGEN, the
nLTE, line-blanketed model atmosphere code of Hillier et al., 1998. The B
supergiant temperature scale derived here shows a reduction of 1000 - 3000 K
compared to previous results obtained using unblanketed codes. Mass loss rate
estimates are in good agreement with predicted theoretical values and all of
the 20 B0 - B5 supergiants analysed show evidence for CNO processing. The
observed WLR values calculated for B0 - B0.7 supergiants are larger than
predicted values, whereas the reverse is true for B1 - B5 supergiants. This
means that the discrepancy between observed and theoretical values cannot be
resolved by adopting clumped (i.e., lower) mass loss rates, as for O stars. The
most surprising result is that, although CMFGEN succeeds in reproducing the
optical spectrum accurately, it fails to reproduce key UV diagnostics, such as
NV and CIV P Cygni profiles, precisely. This problem arises because the models
are not ionised enough and fail to reproduce the full extent of the observed
absorption trough of the P Cygni profiles. These findings add further support
to the need to revise the standard model of massive star winds.
