The soldier had been seriously injured throughout his body with extended hospital stay. He undergoes surgeries and other difficult treatments weekly, to the point that he describes his situation as death would be better than his current life. Traditional painkillers did not help provide relief, but smoking medical marijuana has helped. 

So the injured soldier asked if he would be allowed to smoke his medical marijuana on Shabbos to relieve his pain.

Rav Kook responded that being that he has the status of a sick person in a life threatening situation, a choleh sheyesh bo sakana, he can do whatever he needs, including smoking the marijuana. Rav Kook clarifies that even though the soldier's life is not actually in danger, he is still categorized halachically as being in life-threatening danger due to the type of injuries incurred. 

While there is room to be stringent and some of the earlier poskim prefer stringency in such a situation and only allow chilul shabbos in great need (when there is no actual danger of death), this situation would qualify as great need. Also, it is known that if the patient can be calmed and relaxed it can help him overcome the illness, while his pain makes him weak, in addition to the pain, and deprives him of sleep, making it more difficult to recover. For his healing this would be considered a great need. 

I wonder why he didnt suggest edibles instead of smoking, though perhaps the edibles dont have as much of an effect as the smoking does for the injured soldier.