1) select the 'default' material from the outliner

2) using the RMB on the geometry window, go to the UV Mapping submenu and select 'Force Segment'

3) in the AutoUV Segmenting window start selecting faces on the body and tracks and assigning them to an AUV Chart. I have set all the track sides [selected] to the same chart (yellow), the track faces to another (light blue), the body sides and bottom (pink/purple), and the body topfront and back to another (green)

4) now we are going to set the turret top, front, sides and back to the same AUV Chart, then move to edge select mode and select the 4 vertical edges of the turret. with that done we use the 'Mark Edges for Cut' option. this will cut the UV chart along those lines. follow a similar process for the barrel, select the 4 long faces of the barrel and assign them to the same AUV Chart, then add a cut line to ONE of the horizontal edges (preferably along the bottom side of the barrel). assign the end of the barrel to a different AUV Chart than the rest of the barrel.

5) from the RMB menu, go to the 'Continue' sub-menu and select 'Unfolding'.
