1) Main Gun      

This would be whatever you choose for your usual carry gun, be it full-size or compact, revolver or semi-auto. 
 
2) Back-up or alternate carry gun       

This would be a compact gun for those times when you need to carry light, but it should be gun with enough power to save your butt should the need arise.  An action and operating style similar to the main gun would be helpful.  Simplicity and continuity of training is never a bad thing. 

3) "The gun for when you can't carry a gun." 

Also known as the "church gun." Something very tiny like a Seecamp or P32 for those times when you absolutely can't appear to be armed, yet are not comfortable being totally without a gun.  Not a replacement for the main or back-up gun, just a "hedging-your-bets" gun.  It can also be used as a back-up gun when carrying something larger.

 4) Replacement Gun.         

The author suggested, and I agree 100%, that if you ever shoot someone with your main gun it will be taken by the police as evidence. This is regardless of whether or not your shooting was righteous. As an ex-street cop let me mention that the police do not usually decide who gets prosecuted. The police investigate the shooting, gather evidence, and the if there is the slightest chance the shooter committed a crime they charge the shooter. Ultimately the district attorney's office decides who gets prosecuted and who does not. So if you shoot someone you lose your gun to the cops. Now is not the time to *not* have a gun. Remember, if you shoot and kill some bad guy, there is every chance he will have friends or family that resent your action. Do you really want to be unarmed or armed with something new, unfamiliar, or less powerful than your main gun at that time? 
 
So the replacement gun is to fill in for the main gun at this point. It should be readily available, something you're familiar with, should probably fit your leather gear, and should use the same mag pouches or speedloaders and carriers. 
 
I happen to think the above battery is pretty sensible. I also think that having continuity between guns is a good thing. Although I have revolvers, SA autos, and DA autos, I like to train with one style for most of my practice time. How about you? Do you think continuity matters here? What sort of guns do you have that would meet the four gun battery criteria?

Author's note, May 2007: since I wrote this a few years ago I've rejected the four gun battery as my personal approach.  The idea that a mini-gun chambered for a subcaliber round can ever serve to replace a gun of serious power has come to seem absurd to me, and these days the smallest and lightest guns I will carry are the likes of my Glock 27 .40S&W and my Taurus 9mm snub revolver.

copyright 2003 by the author, all rights reserved.