Need help for Sci-fi Book

I read a sci-fi /military novel about a decade or so ago and I'm trying to figure out its name.

The characters are cyborgs, (were humans on deathrow that were given the option to donate their bodies/minds as soldier grunts instead of death).

Most vividly there was a Tank-type cyborg main character who had a bullseye painted on his chassis. That is probably the most specific thing I know.

Any Help?

there were grunt soliders, and then the Tank-ones were four legged pods.