  At 327 MHz, the observed emission of PSR B1937+21 is greatly affected by
scattering in the interstellar medium, on a timescale of order the pulse
period. We use the bright impulsive giant pulses emitted by the pulsar to
measure the impulse response of the interstellar medium and then recover the
intrinsic emission of the pulsar by deconvolution -- revealing fine structure
on timescales not normally observable. We find that the intrinsic widths of the
main pulse and interpulse in the pulse profile are similar to those measured at
higher frequencies. We detect 60,270 giant pulses which typically appear as
narrow, ~100 ns bursts consisting of one to few nanoshots with widths $\lesssim
\! 10$ ns. However, about 10% of the giant pulses exhibit multiple bursts which
seem to be causally related to each other. We also report the first detection
of giant micropulses in PSR B1937+21, primarily associated with the regular
main pulse emission. These are distinct from giant pulses not only in the
phases at which they occur, but also in their larger widths, of order a
microsecond, and steeper energy distribution. These measurements place useful
observational constraints on emission mechanisms for giant pulses as well as
the regular radio emission of millisecond pulsars.
