We’ve found a really great online collection called Prints, Drawings and Watercolors from the Anne S. K. Brown Military Collection, hosted by Brown University. Here you can find a digitized collection of military and naval history art. Read about the collection.
The images are fantastic and the viewer allows you to see the incredible details through the zoom options. You can also download and save images. The collection is growing and eventually will contain over 15,000 images. This is a fantastic historic resource with so much to explore!