Let's start modelling the torso. Select one half-helmet, enter Edit mode,
and, Add-Mesh-Icosphere, with the default 2 Subdivision, and place it like
in the image above.
In Side view, enter Edit mode, select the half back of the sphere vertices
and delete them.
In Top view, with the PVE, O key, select the left back vertices of the sphere
and move them to the back ( see image above).
In Front view select the four lower vertices of the sphere and Extrude down
.
To model the top side of the torso, select the lower vertices at the back
of the helmet (image above), Copy and Move them down a little bit. Extrude
one time.
With the 3D cursor always at the center of the object, enter Edit mode,
Add-Mesh-UVSphere with 16 Segments and Rings. I know, it's a "crazyness"
but it's for a good cause.
In Front view, select all the sphere vertices, (select one vertice of the
sphere, put the mouse cursor over the sphere and press L key), and turn
them 90º. Select the top half sphere vertices and delete them. Select
the right half and delete it.
Select the far left row and delete either ( look at the images above to
guide you), and reshape.