Since I covered shields pretty much ad nauseum, I thought I'd move on to helmets. For most of the same reasons that the shield didn't get it's proper respect, the helmet got screwed over by D&D rules too; the designers of the game simply had no real experience of the helmet's importance in keeping combatants alive. I have said in the past that if I had to choose 2 out of 3 armor parts, Shield, any type of body armor and Helmet I would 100% of the time pick Shield and Helmet. You all know why I would pick the Shield from my series of Shield posts, this is for the poor Helmet. Here's a little known fact, most of the time in mêlée combat you get hit in the head. That's just where shot's get through. Here's another little known fact, even the crappiest helmet is still pretty darned good at stopping blows from killing you. Yet for some reason there are either no rules, or at best, very obscure rules, in ANY addition of D&D (that I am familiar with, I guess 4e might have some) regarding Helmets at all.
What's worse is that in 1st edition AD&D there are two types of helmet listed on the equipment list- Helmet, Great and Helmet, Small for 15 and 10 Gold Pieces respectively with absolutely no benefit listed for owning either of them, nor a description of either type of helmet. So why should any player waste his starting money on a Helmet? It takes a pretty sharp-eyed DM to find the rule about characters fighting without wearing helmets in the DM's Guide; I know I have seen it before and I went looking for it and couldn't find it to cite it here. Something about the head being AC10 with no helmet and intelligent monsters taking advantage of that. There was also a rule about a certain percentage of all shots in mêlée being head shots, 1 in 10 I think, but nobody ever used it because it slowed down combat and you had to remember your head's AC too. I think the Great Helm was AC 3 and the Small Helmet AC 5, but I may be mixing editions.
Checking the 2nd edition AD&D Player's Handbook equipment list shows the problem is exactly the same, only worse. There are still only two types of helmet listed, one of them is still the Great Helm which has increased in price to 30 Gold Pieces (inflation, what can you do?); the other though is, inexplicably, the Basinet (which, by the way is not the most common spelling for this helmet type, it is usually spelled Bascinet), and at the bargain price of 8 Gold Pieces, which makes no sense whatsoever to anyone who knows anything about helmets. Great Helms only SOUND more impressive, Bascinets are a vast improvement in the art and science of armoring; it takes way more time and skill to make a Bascinet than it does a Great Helm.
Which leads us to a little history lesson on the timeline of helmet types starting in antiquity and ending in the late middle ages. The earliest helmet types are usually in one of two styles, with a number of various options that can be applied, for simplicity's sake I am going to refer to them by the general term "Spangenhelm" which sounds German to me. I don't know where it comes from, probably archeology, and it probably is called other things when it's not found in a western European context, but I want this kept simple so that's the name I am using. Spangenhelms come in either the round-top or conical varieties. Some of the additions possible were longer backs and sides to protect more of the head than just the top, or a nasal guard, or oculars (circles that come down and protect the eyes, kind of look like glasses), or cheek guards or chainmail "veils" to protect the face, or a chainmail "scarf" to protect the neck*. This type of helmet was in use from the Roman legions to the Saxons that invaded Britain to the well dressed Viking. You can see them in use on the Bayeux tapestry on both sides of the Battle of Hastings.
The main purpose of the helmet is to keep the axe, sword, mace, club or whatever that you let slip past your shield from caving in your skull and making you dead. Trust me on this, most blows that make it past your shield WILL hit you in the head. The Spangenhelm mainly does this by deflecting the blow across it's rounded surface and absorbing the force of the blow across a greater area than just, say, the edge of a sword. Unfortunately for the Spangenhelm, unless this blow comes from above, it will find a relatively flat surface to bite into. This will be a recurring theme in helmet design as weapons get better, helmets (and body armor) begin to match pretty shortly.
The Spangenhelm had a good run as armor types go, but eventually weapons and tactics got better and it was replaced. The mighty Great Helm had arrived. That's just it's coolest name, it's also known as the Pot Helm, Bucket Helm and Barrel Helm; an even cooler looking late variant is known as the Sugarloaf Helm. These are the helmets that Crusader knights were wearing and what most of us think of when we think of a knight's helmet. I don't know what armorer had the neuron fire that made him decide to make a helmet that actually covered the face and mostly protected the eyes, but this was seriously brilliant thinking; and just in time since knights had really just started doing heavy cavalry charges at each other with lances. Sadly, despite it's vast improvement in overall protection, the Great Helm still has relatively few glancing surfaces, and in fact** you lose the rounded/conical top of the Spangenhelm, which was it's greatest feature.
In the SCA, the flat top of the Great Helm is known as the "Landing Strip". Seriously, I own 3 Great Helms, I have a love/hate relationship with them all. I always wind up going back to the ugly one, the one that was home made by a buddy of mine. It was his first helmet, it's heavy gauge steel (14 sides/12 top) and has a bar grill welded to the front for better ventilation and visibility. When he got rid of it I bought it off of him and it was my first helmet, aside from the Delftwood loaner gear. It's the one I am wearing in all of my fighting pictures. The others are prettier but don't fit my giant head as well with any padding at all and their visibility is less, although not as bad as you might think and their ventilation isn't great either, but that isn't so much a breathing thing as it is a cooling down thing. The landing strip isn't a real big deal for me because I am really tall and a Great Helm sits even higher on my head.
Now, the Bascinet, which is what all the cool knights are wearing from the 14th century on until the end of the classic D&D period. Since it comes along at roughly the same time as "Full Plate" and "Field Plate" more or less, maybe it should be excluded from discussion, but the absolute melange of periods in D&D is more or less the same as in the SCA, only the SCA has fewer elves***. Anyway, the Bascinet is, more or less, the epitome of the armorer's art in the making of helmets. It is designed with curves everywhere, meaning that the entire damned thing is one big glancing surface covering your melon. If you know how to move with a blow at all, to roll with it, nothing sticks to your head. Fine helmet. Wish I could afford one. Sadly, Bascinets are really all custom jobs. I do some metal work and have made some simple armor parts, this is WAY beyond my skill level. I know a good helmet guy that can do Spangenhelms and Great Helms, he would never attempt to make a Bascinet. So the Bascinet getting it's only mention in an AD&D book as the cheapest helmet of them all is basically ludicrous.
OK, here comes another caveat about the SCA: in the SCA we cheat on helmets, because of our safety features we can use bar grills instead of covering our faces for protection in sheet steel. As I mentioned above this provides better visibility and ventilation, it also makes the Spangenhelm a more viable choice of helmet, essentially the same as a Great Helm protection-wise because it now has a bar grill welded over the face, something it never had back in the day. We also open up the faces on our Bascinets and our Great Helms, although if you can afford a Bascinet you usually get the historical visor that can switch out, we have some tournaments that are exclusive for very period kits. Some guys that have pre-14th century personae in the SCA (that's like your character, except really it's just you), like say, Vikings, have Bascinet helmets retrofitted to look like a Spangenhelm, but actually perform like a Bascinet.
I was reading recently on one of the OSR blogs saying Gary meant for D&D to be early medieval, they had a link to the armor book he used for his source. It was old and outdated, but at least it's a bit of history telling us where EGG got his information from. I am pretty sure he intended that D&D be pretty early medieval anyway based on the AD&D "Gold Box" miniature line from Grenadier, looking at them sitting on the shelf above my computer as I write this I see pretty much all of the guys are wearing Spangenhelms and the weapons and shields are 11th century at the latest. It was his Swiss fixation on polearms that threw a monkey-wrench into the works. Other than that the aesthetic for AD&D seems to be circa turn of the 1st millennium, certain popular pieces of 1st edition AD&D artwork notwithstanding. I can only assume from the evidence of the official AD&D miniature line that the Small Helmet of the 1st edition AD&D Player's Handbook is actually a Spangenhelm
*There are actual technical terms for all of these things, but I am trying to keep things simple; please don't be insulted by this, I just don't know how much technical jargon will be OK here.
**With the exception of the Sugarloaf Great Helm, which is considered a "transitional" helmet to the Bascinet.
***None actually, not officially anyway, we are an educational organization after all, not a LARP; I have heard tales of people who refuse to play the game by the same rules as everyone else and decide that they are an elf, or a vampire or a member of a Starfleet away team or whatever. I have never seen them, but I have heard the tales. My guess would be that they realize they're at the wrong place and move along eventually.