need advice

I am a work center supervisor in U.S. Navy. I have 5 people working immediately under me. One of these people seems to have a psychological problem. He doesn't seem to be very asscoiative with other people. He always wants to be by himself. He can't concentrate on any tasks that I give him. This creates stress on everyone else because they have to pick up the slack. But he other times gets laser-like concentration and gets tasks done incredibly fast and efficently. There doesn't seem to be any consistency in these periods of concentration. He is really smart though, and can answer pretty much any question I ask him. He reads occupational related material alot. He seems to enjoy it.
The problem is, this job is primarily evaluation based. He has all this knowledge, which sometimes helps me out, but can't seem to do any job I give him with consistency. I really don't like watching people who work for me have an awesome chance to advance, but can't do it in spite of themselves. Does anyone have any advice on how I can get him to perfrom better on jobs I give him. I'd really apprecate it.
This job is primarily mehanical. Specifically dealing with HVAC.

Hey Mike, you got a base health/psychological center you could send him to for educational and psychological testing? He could have an attention problem or a mild learning disorder or something. Can you track down how he learns best? Maybe if he had videos to learn from or if you broke down and wrote out the steps he was supposed to do (since he likes to read). But I'd find where to have broad tests done to see if there's a way he can learn better than others. See if you can find anything here?

http://www.nlm.nih.gov/medlineplus/l...disorders.html

Perhaps he is bored with the job as it might not be challenging/intriguing enough for him anymore. He might possibly have ADHD or be depressed.

Problem with being enlisted is that being diagnosed with anything can interfere with your career. On the outside, stigma exists... but as I'm former Army myself, I know how different it is in the military environment. He doesn't need a label slapped on him, and military doctors are more interested in giving Motrin anyway.

Have you ever asked him in private and in a manner that isn't authoritative or judgmental why he is so inconsistent? If he likes his job? If maybe he has girlfriend issues, etc? There is probably some way of identifying the problem and helping him to motivate himself.

I was depressed with my job in the Army, and also trapped in it. Your job seems more interesting than mine was though, because at least what you do is real and has real results.

Have you talked with him? Let him know you would like to know how to help him to be able to have more focused and productive times and see what he might suggest? Let him know that sometimes he seems very much more focused than other times and ask if he knows why that is. (Is it motivation, insecurity, lack of knowledge...).
Let him know where you'd like him to be and get him on board to help come up with a way to make that happen. That will also let him know that you have expectations, that you are willing to help, but it is up to him to stay motivated and to do his work efficiently and well.

You know, sometimes people get caught in a loop where they feel like they are constantly not good enough and evaluated poorly and can never do anything right, and so they keep getting more and more negative feedback, which makes it that much harder to improve their performance. What if you make a point to catch him doing something right at least once a day and tell him what he is doing right? Then you can build on that.