Through certain actions in the world, things such as new attachments for your weapons become available to buy in store, improving the capabilities of said weapons when purchased. (consoleob.com)
He didn't say weapons are bad and he didn't send the person that struck the guard to hell. (religion.blogs.cnn.com)
New weapons are unlocked first by spending research money on their division, and then spending more money and precious metal (hidden in each stage) to manufacture said weapons. (hardcoregaming101.net)