'to design a process that transforms convicted criminals into expendable assets without compromising their effectiveness'
Seems to me that process has already been thoroughly developed. It is directly from the training manual of the US Marines for 'conscripted' (involuntary, drafted) recruits.
Step 1: Haul them off in buses or other mass transit to a completely contained facility where contact with the outside world is impossible, and the ability to completely control every aspect of their lives is assured.
Step 2: Put them in barracks and force them to wear uniforms that strip all sense of individuality from them, leaving only a collective herd identity.
Step 3: Force them into humiliating situations including hazing, washrooms without any sense of privacy, scrubbing toilets with a toothbrush, mass showers in crowded conditions, sleeping in beds that offer no privacy, and generally continuing to strip them of any concept of individuality, self-respect, individual shame, and control over their lives. Follow this with dehumanizing, humiliating constant barrages of verbal abuse from the herd authority that their survival depends upon.
Step 3: Control their diet completely - everything they eat is closely monitored, and choice is completely minimized to eat or starve. Supplying their basic needs is completely dependent upon the herd organization, and all other needs are deemed inconsequential.
Step 4: subject them to collective, regimented, and synchronous physical exercise that absolutely exhausted them, to the point where they do not have the luxury to think. They just do what they are told, what everyone else is doing, in a synchronized autonomous obedient routine.
Step 4: Repeatedly put them in scenarios where their life is completely dependent on what others do, and instilling the sense that what the lives of their fellow conscripts depends on them following orders and conforming to the herd.
Step 5: Subject them to training exercises that promote a controlled PTSD 'perpetually dazed but not entirely broken' state in them (loud sudden bangs, near-death training scenarios, live fire bullets, sudden awakening by loud alarms and loud shouting) such that they accept that surviving is totally beyond their control, and their survival is entirely dependent on following orders like automatons.
Step 6: Continuous indoctrination that they are doing this 'for loyalty and subservience' to a greater herd cause - perhaps country and flag, and totally replace any other source of self-esteem with a simple 'loyalty to herd'.
Step 7: Once all sense of humanity, individuality, and sense of moral judgement and personal identity is stripped from them, re-program them with the belief that absolute adherence to herd authority is the only way that they can manage and cope with the stress part of PTSD. A controlled, systematic variation of the Stockholm syndrome
Step 8: Once their humanity is stripped from them; they have been reduced to automatons through fatigue, continuous physical exhaustion, and pain; they have been conditioned to absolute obedience to authority; they have replaced any sense of individual goal with loyalty and fidelity to the goal of the 'greater cause'; and they absolutely believe that they are doing all of this of their own free will for the benefit of the collective good of some overriding supreme authority, the only thing left in their psyche is the basic human 'herd animal' conform to the group instinct and response.
Step 9: Once they have been completely reduced to the fundamental herd mentality thinking that is basic and ingrained in humans through evolution, completely indoctrinate them with the ingrained belief that, if they do not conform, they are a complete failure to themselves, their fellow companions, their family, their country, to everyone that has ever mattered to them, and the only way they will NOT be an absolute total failure is to conform entirely to the herd.
Step 10: Now start to train them with the activities that you will praise them for, give them rewards for doing, build their esteem back up, give them a sense of purpose in life, give them a sense on not failing, and in general instilling in them that success in these goals is the only thing that matters to them (including activities that include using weapons of mass destruction against innocents), that will determine their status in the herd.
Result: Highly trained automatons that will do anything on command, all while shouting slogans of 'for flag and country!!!' (basic loyalty to the herd) and actually believing that what they are doing is what they WANT to be doing, what hey have CHOSEN to do.
This has always, throughout human history, been a really cheap way of producing expendable assets for military activities. It is also a very effective way of producing compliant, easily managed, but very productive slaves.
Your embellishment 'this punishment is exclusive to convicted criminals' is a non sequitur, since it has always been used throughout human history without any restrictions as to its application to 'convicted criminals'.
It's all about reducing humans back to the evolutionary ingrained herd mentality, or 'conformation to the herd' that (despite everything that humans may believe or want to believe about notions of human free will and self-determination) is basic to human genetics, and is all that is left once the upper layers of 'civilized behavior' and 'intellectual thought' have been stripped away.