Joshua,
Given that you are in the navy it sounds like underway alot, I assume you have a fair amount of private time when off-duty underway. There are a few things that you can do to make money in SL. Things that you can work on while underway as long as you have access to a decent computer and the software.
Does the Navy provide you with internet access while underway, I would be surprised if it does not these days. As long as you can access the internet you can do the following things.
Software: Photoshop is the premium software but very expensive. Paintshop Pro is very good and reasonably priced. Gimp is free and will do almost anything you will need.
Textures: someone already mentioned that... you will need graphics software that can do layers and alpha textures. Photoshop is the premium software but very expensive. I get by with Photoshop Elements V2.0, an old version I got cheap. Paintshop Pro is very good and reasonably priced. Gimp is free and will do almost anything you will need.
Clothing: is really a subset of textures, but there is a shortage of good men's clothing in SL, at least realative to women's clothing. To to the
Design and Textures Forum and read the Sticky tutorials on how to make clothing.
Scripting: This is hard to learn and you will need to access SL often to test scripts out expecially while learning, but once you begin to understand it, you may be able to do alot of work while offline. I recently read in the
Scripting Tips Forum that there is an offline compiler you can get or access via the web to test that your scripts will compile when you cannot log into SL.
Building: You can't aquire many building skills without spending time in SL learning and doing. But you can use programs like Maya to develope 3d building skills and learn to make and apply textures to buildings that can be baked and dowloaded then uploaded into SL to apply extremely realistic lighting effects to SL builds. Someone is even working on software that will allow a person to build objects off line then import them into SL. I think it is a only a matter of time before this is a real possibility.
Sales: You don't even need to set up a shop in SL to sell this stuff ( which involves renting or buying land), you can sell it on SLExchange.com or SLBoutique.com and possibly a few other sites.
Quality and customer appeal: Just because you make something does not mean it will sell. There are a lot of horribly made, tawdry products for sale in SL, and many disappointed product creators who thought "If you make it they will come". It is not true. your product has to have appeal and be of decent quality or you are wasting your time.
So.... there are things you can do to acquire skills, and create things that can be sold in SL to make money using your spare time. There is nothing you can do to make money in SL that does not require a considerable investment of time and effort: 1. to acquire the skills; and 2. to create things to sell.
Someone once said most people can make more money selling MacDonalds hamburgers then they wil ever make in SL. That is true at least initially regarding the payback you can get for an hour of time invested. However, once you have created a body of selllable items, they do not deteriorate, and you can keep selling them over and over again indefinitly.
IT MAY TAKE TIME: I have been in SL for 18 or so months, I have created lots of things and have been selling them for most of that time. My business has grown slowly but for the last 4 months I have cleared significant amounts above and beyond my land tier costs. It is finally enough to justify my continuing to do this.