Here's what makes him dangerous.
He's very sensitive to noise. Anything a speaking voice or above causes him to go into an insane, violent rage. He also reacts to quick movement and anything that can be perceived as a threat. If he sees violence, he's likely to respond violently. He is also very sensitive to light, which is why his containment area is very dim. He looks frail, but he actually has the brute strength of multiple large gorillas in one, and he moves at very high speeds, maxing out at about fifty miles per hour in a full sprint. He has an excellent memory.
Containment:
The War Vet is contained in a very specific manner in order for him to not be 'triggered'. He is contained in two soundproof rooms. The first room is 20 feet by 20 feet, a safeguard so when transferring to his room he can't hear noise from outside. The second room, the one he is contained in, is 15 by 15 feet. Both rooms have only very dim lighting.
Containment procedures:
When entering the War Vet's containment room for cleaning or feeding, be very cautious. Due to his pure strength, at least 5 security personnel need to be in the room at all times. First, you enter the 20 by 20 room, and shut the door behind you. This way, no noise from the outside leaks into the actual 15 by 15 enclosure. Then, when entering the main containment area, open the door very slowly, and call out the the SCP in a whisper. Make sure he knows you're coming in. This seems to calm him.
Enter the 15 by 15 enclosure one by one and shut the door behind you, also slowly and carefully. Make sure while near the War Vet talk in only a whisper. Try and ignore him while you clean the area and leave behind food. Usually he isn't social, and he'll just sit in the corner. However sometimes he tries to make a break for the exit, and if he does this then simply draw your tranquilizers. Remember, when you enter the containment area always have one designated shooter with a taser, one with a tranq, and one with an actual weapon. The tranq may take some time to come into effect, and if that is the case, then tase the SCP and have all five of those in the room hold him down until he falls asleep. Please try to keep him as calm as possible, because his memory seems to be infinite. If he attacks a group of security and they make it out alive, those security aren't allowed to stay with him anymore, for he'll remember their faces. He also adapts, and every time he is contained he comes up with a new strategy to escape.