  $SU(2)$ gauge fields can generate large gravitational waves during inflation,
if they are coupled to an axion which can be either the inflaton or a spectator
field. The shape of the produced tensor power spectrum $\mathcal{P}_h$ depends
on the form of the axion potential. We derive analytic expressions and provide
general templates for $\mathcal{P}_h$ for various types of the spectator axion
potential. Furthermore, we explore the detectability of the oscillatory
feature, which is present in $\mathcal{P}_h$ in the case of an axion monodromy
model, by possible future CMB B-mode polarization observations.
