SCUBA and AMBO surveys at ~1mm have revealed the presence of a rich class of 
high-redshift powerful starbursts, ultra-luminous in the far-infrared 
("submillimeter galaxies", SMGs). They are probably the progenitors of present 
day massive elliptical galaxies, caught at the epoch of one of their most 
important merger events. This field is now revolutionized by the wide-field 
surveys carried out by space observatories: 1) Spitzer and Herschel have 
increased the area observed by two and soon three orders of magnitude, 
respectively; 2) the submm bands of Herschel provide direct information on 
the far-infrared luminosity and the star formation rate of such galaxies.  I 
will focus my talk on the results of the detailed study we are completing on 
the z~2 ultra-luminous massive starburst galaxies selected by Spitzer in the 
mid-IR (24um-bright '5.8um-peakers').  Spitzer thus allows the selection of 
more than 100 z~1.5-2 ULIRGs per deg2, in ~70 deg2, with a far-IR luminosity 
approaching 10^13 Lsun/yr (SFR~1000 Msun/yr), including a large fraction of 
z~2 SMGs. Focussing on a complete sample in the 'Lockman-North' Field (0.5 
deg2), we have shown their high detection rate at 1.2mm with MAMBO; checked 
their far-IR luminosity with 350um SHARC2/CSO observations and through the 
radio/far-IR correlation; studied in detail their prominent mid-IR PAH 
spectrum and checked its correlation with the far-IR emission; and begun 
their CO study.  These sources are remarkably well detected by Herschel/SPIRE, 
even with the relatively shallow sensitivity of most HerMES widest fields. I 
will present a preliminary analysis of the far-IR emission of 5.8um-peakers in 
Lockman-SWIRE Field; its correlation with 24um emission; and the prospects 
that such sources offer for studying z~2 massive galaxies, their evolution, 
star formation and clustering.