War neuroses (shell shock) is the reaction of some WW1 soldiers to the trauma of battle. More selectively it is a reaction to the intensity of constant bombardments that produced a helplessness appearing variously as panic, flight, uncontrollable shaking or gait, an inability to reason, sleep, walk and/or talk.
"Simply put, after even the most obedient soldier had enough shells rain down on him, without any means of fighting back, he often lost all self control."
For many shell shock is defined as the precurser to PTSD. PTSD was influenced by the experiences of psychiatrists working with veterans returning from Vietnam. As such the two ideas set out to do pretty much the same thing. The select difference however is that shell shock was specific to the experiences of concussive shelling whereas the concept of PTSD was developed and stems from a wide range of combat experiences.
Though both implications can now be listed under PTSD they are different in how they present. For example, to fulfill the criteria for re-experiencing and arousal a shell shocked person may present with physiological reactivity, hypervigilance, uncontrollable shaking, staggered gait, and an exaggerated startle response whereas a more general PTSD case may present with intrusive and distressing recollections, bouts of irritation and anger, as well as difficulty sleeping and concentrating.
Today both would receive the same diagnosis of PTSD but the first description seems much more resonant with the idea of shock and fear conditioning whereas the second seems to be more of a depressive reaction. These two forms of PTSD would indeed seem to be, psychologically, very different experiences.
Some researchers go even further to proclaim that cases of shell shock are more inline with actual neurological damage due to the shellings concussive force on ones body and mind. No studies in modern day history can supports such claims though as cases of study are no longer produced on the modern battlefield.