  We report the first observation of diffractively produced W bosons. In a
sample of W -> e nu events produced in p-barp collisions at sqrt{s}=1.8 TeV, we
find an excess of events with a forward rapidity gap, which is attributed to
diffraction. The probability that this excess is consistent with
non-diffractive production is 1.1 10^{-4} (3.8 sigma). The relatively low
fraction of W+Jet events observed within this excess implies that mainly quarks
from the pomeron, which mediates diffraction, participate in W production. The
diffractive to non-diffractive W production ratio is found to be R_W=(1.15 +/-
0.55)%.
