  We thoroughly explore the properties of (sub)-millimeter (mm) selected
galaxies (SMGs) in the Shark semi-analytic model of galaxy formation. Compared
to observations, the predicted number counts at wavelengths (lambda) 0.6-2mm
and redshift distributions at 0.1-2mm, agree well. At the bright end (>1mJy),
Shark galaxies are a mix of mergers and disk instabilities. These galaxies
display a stacked FUV-to-FIR spectrum that agrees well with observations. We
predict that current optical/NIR surveys are deep enough to detect bright
(>1mJy) lambda=0.85-2mm-selected galaxies at z<5, but too shallow to detect
counterparts at higher redshift. A James Webb Space Telescope 10,000s survey
should detect all counterparts for galaxies with $S_{\rm 0.85mm}>0.01$mJy. We
predict SMG's disks contribute significantly (negligibly) to the rest-frame UV
(IR). We investigate the 0<z<6 evolution of the intrinsic properties of >1mJy
lambda=0.85-2mm-selected galaxies finding their: (i) stellar masses are
$>10^{10.2}M_{\odot}$, with the 2mm ones tracing the most massive galaxies
($>10^{11}M_{\odot}$); (ii) specific star formation rates (SFR) are mildly
(~3-10x) above the main sequence (MS); (iii) host halo masses are $\gtrsim
10^{12.3}M_{\odot}$, with 2mm galaxies tracing the most massive halos
(proto-clusters); (iv) SMGs have lower dust masses ($\approx 10^{8}M_{\odot}$),
higher dust temperatures ($\approx 40-45$K) and higher rest-frame V-band
attenuation (>1.5) than MS galaxies; (v) sizes decrease with redshift, from
4kpc at z=1 to <1kpc at z=4; (vi) the Carbon Monoxide line spectra of $S_{\rm
0.85mm}>1$mJy sources peak at 4->3. Finally, we study the contribution of SMGs
to the molecular gas and cosmic SFR density at 0<z<10, finding that >1mJy
sources make a negligible contribution at z>3 and z>5, respectively, suggesting
current observations have unveiled the majority of the star formation at
0<z<10.
