  We present a 60 ks Chandra ACIS-S observation of the isolated edge-on spiral
NGC 3556, together with a multiwavelength analysis of various discrete X-ray
sources and diffuse X-ray features. Among 33 discrete X-ray sources detected
within the I_B = 25 mag per square arcsec isophote ellipse of the galaxy, we
identify a candidate for the galactic nucleus, an ultraluminous X-ray source
that might be an accreting intermediate-mass black hole, a possible X-ray
binary with a radio counterpart, and two radio-bright giant HII regions. We
detect large amounts of extraplanar diffuse X-ray emission, which extends about
10 kpc radially in the disk and >~ 4 kpc away from the galactic plane. The
diffuse X-ray emission exhibits significant substructures, possibly
representing various blown-out superbubbles or chimneys of hot gas heated in
massive star forming regions. This X-ray-emitting gas has temperatures in the
range of ~ 2-7 x 10^6 K and has a total cooling rate of ~ 2 x 10^40 erg/s. The
energy can be easily supplied by supernova blast-waves in the galaxy. These
results demonstrate NGC 3556 as being a galaxy undergoing vigorous disk-halo
interaction. The halo in NGC 3556 is considerably less extended, however, than
that of NGC 4631, in spite of many similarities between the two galaxies. This
may be due to the fact that NGC 3556 is isolated whereas NGC 4631 is
interacting. Thus NGC 3556 presents a more pristine environment for studying
the disk-halo interaction.
