  We have mapped the powerful radio galaxy Hercules A at six frequencies
spanning 1295 to 8440 MHz using the VLA in all four configurations. Here we
discuss the structure revealed in total intensity, spectral index,
polarization, and projected magnetic field. Our observations clearly reveal the
relation between the bright jets, radio source. The jets and rings form a
coherent structure with a dramatically flatter spectrum than the surrounding
lobes and bridge, strongly suggesting that they represent a recently renewed
outburst from the active nucleus. The spectrum of the lobes is also steeper
than in typical radio sources, and steepens further towards the centre. The
compact core is optically thin and also has a remarkably steep spectrum (alpha
\~ -1.2). There is some evidence that the old lobe material has been swept up
and compressed ahead of the new outburst. We interpret the dramatic asymmetry
in the bright structure, and more subtle differences between diffuse lobe
structures, in terms of relativistic beaming combined with front-to-back
light-travel delays which mean that we view the two lobes at different stages
of the outburst. After correcting for Faraday rotation the projected magnetic
field closely follows the edge of the lobes, the jets, and the rings; the field
pattern in the two lobes is broadly similar. We confirm a strong asymmetry in
depolarization and Faraday rotation, with the jet side the less depolarized and
the flatter spectrum, consistent with general correlations between these
asymmetries. The spectral index asymmetry is clearly present in the `old' lobe
material and so, at least in this case, is not due to beaming; but it can be
understood in terms of the light-travel delay.
