What Makes a Good Tank?

M4A4 Cutaway: 1 – Lifting ring, 2 – Ventilator, 3 – Turret hatch, 4 – Periscope, 5 – Turret hatch race, 6 – Turret seat, 7 – Gunner's seat, 8 – Turret seat, 9 – Turret, 10 – Air cleaner, 11 – Radiator filler cover, 12 – Air cleaner manifold, 13 – Power unit, 14 – Exhaust pipe, 15 – Track idler, 16 – Single water pump, 17 – Radiator, 18 – Generator, 19 – Rear propeller shaft, 20 – Turret basket, 21 – Slip ring, 22 – Front propeller shaft, 23 – Suspension bogie, 24 – Transmission, 25 – Main drive sprocket, 26 – Driver's seat, 27 – Machine gunner's seat, 28 – 75 mm gun, 29 – Drivers hatch, 30 – M1919A4 machine gun.
(Source)

I know, I know, probably some of you are groaning already, "Sarge, really? Another tank post?"

Yup, I like tanks, a lot. (Seems I've mentioned that a time or two over the past couple of weeks.) While I won't say that this is "Tank Week," it could turn out that way. Because, again, I like tanks.

But I know some of you (I'm looking at you Beans, probably Paul as well) would like to chime in on what makes a good tank. I was going to do a "good tank, bad tank" sort of post, but the research on those takes a while, I mean there's reading, there's comparative studies, field testing, and the like to write a really authoritative "good tank, bad tank" post. As I have a job which pays the bills and keeps The Missus Herself happy (mostly by keeping me busy most of the day, and the week for that matter), I can't research and post stuff all the live-long day. (To quote an old railroad song...)

Before going further, just what is a tank, or armored fighting vehicle, if you prefer? Well, a tank:

1. has a turret capable of movement through a 360° arc.
2. has a cannon mounted in the turret. The Swedish S-Tank notwithstanding, more formally known as the Stridsvagn 103, a superb design for use in Swedish terrain, it's lack of a turret makes it, in my book, a tank destroyer, rather than a true tank. For those who need to know such things, stridsvagn is Swedish for "fighting vehicle."
3. is (duh) armored. Not just covered in steel, armor is a special kind of steel. The M-1 Abrams is wrapped in what is called Chobham armor, which is, simply put, a composite of different materials, including ceramics, steel, and other stuff which is classified. Not even your beloved Sarge knows what's in it, you can read more about that here. Should you enjoy that sort of thing.
4. runs on tracks. Rather like you'd see on a bulldozer. Why? Tracks are very good on rough ground, a tracked vehicle can go places a wheeled vehicle has trouble with. (No doubt I'll get an argument from Beans on that, he so loves his armored cars.)
5. carries a crew used solely to operate the vehicle and fire the main gun. It doesn't carry infantry, while the M-2 Bradley might look like a tank. It ain't a tank.

Bradley Infantry Fighting Vehicle
Looks kinda like a tank, is not a tank.

So what should one look for in a tank? (Should you decide to motor on down to the used tank lot this weekend, these tips might help.)

The "big five," as I like to call them are:

1. Firepower,
2. Mobility,
3. Protection,
4. Maintainability, and
5. Usability.

Firepower isn't just how big the cannon in the beast is, but also how effective the cannon and its accompanying optics and support equipment are. It also takes into account the muzzle velocity of the ammunition it fires, primarily armor-piercing but you want some high explosive stuff as well to discomfit enemy infantry and soft vehicles, as in trucks and cars. A general rule of thumb is that faster is better. Remember your high school physics classes?

kinetic energy (K.E.) = 1/2 times the mass times the velocity squared

The kinetic energy is how hard you punch the target (enemy tank). The mass in this case is the mass of the projectile being fired at the target (heavy is good, dense is really good, you can get a heavier projectile which is smaller in size, so you can carry more of them, for one thing), The velocity in this case is the muzzle velocity mentioned above, how fast the projectile leaves the barrel of the gun. (Think in terms of thousands of feet per second.)

How hard you can hit and from how far away makes for a very dangerous tank. The optics are important, if you can't see a target at longer ranges, your gun, no matter how powerful, isn't as useful.

Support equipment in modern tanks can mean the computers and software used to aim and fire the cannon. But in all tanks it's also how much you can raise and lower the main gun, how fast you can turn that turret. How much ammunition is carried for that big gun (and how and where it is stowed in the tank) is also what I would call support equipment. Remember that main gun is the whole reason for the tank's existence. (Which is also partly why the Bradley isn't a tank, the gun is far too small. Though very effective for its intended purpose.)

Mobility is important because you want to be able to move quickly over rough terrain. Roads are nice but the enemy doesn't stick to the roads, neither should your tanks. How good the tracks and their associated running gear on a tank are is an important consideration. Will the tracks break or fall off in a turn? How long will they last before having to be replaced? If something breaks, how quickly can the crew fix them? Oh wait, I've wandered into #4. We'll get to that. Also how good is the engine that drives those tracks? Does it guzzle fuel like a drunken sailor? (What do we do with those?) How far can it travel on a single tank of fuel? (While tanks aren't meant to travel long distances, they do tend to cover a lot of ground in battle. You don't want to "run out of gas" at noon when the fight lasts until suppertime.)

Protection means armor. It can't be thick everywhere otherwise the tank is going to be very heavy and the engine would need to be really, really powerful. Powerful engines drink a lot of fuel and take up a lot of space. So you put the armor on places it is most needed, like on the front of the tank, the part facing the enemy. Yes, yes, the enemy will get on your flank from time to time, he'll get behind you, and (heaven forbid) he'll be above you at times. (If you're really unlucky, he'll be in an A-10. Seventy years ago he would have been in a Ju-87, P-47, or Il-2 Sturmovik, all of which will be the subject of a future post. Think near future. Hhmm, maybe it is Tank Week.)

You need to protect the crew first and foremost, I mean they're the ones who operate the tank, a tank with no crew is just a big expensive "piece of steel," more or less. You also need to protect the engine, and that big cannon, and the other stuff inside the tank. You can use thinner armor if you angle the plates, which increases the relative thickness of the armor.

Par exemple -

For an armor plate of given thickness, increasing the slope increases the relative thickness. As shown here.
(Source)

Maintainability is another important factor in what makes a good tank, and I mean maintainability in the field, by the crew. If they can't fix their tank when it breaks (and trust me, it will break) then you need to haul it back to a maintenance shop, often well in the rear. The crews need to be able to fix things on their vehicle with what they have on hand. Which is why you see all sorts of stuff carried on the outside of a tank: crowbars, jacks, shovels, spare bits of track, and other things to keep the beast running.

Usability means many things to me. Is the interior of the tank well designed? Are the crew members comfortable, are the things they need to do their jobs readily to hand? How hard is it to operate the tank, as in driving it, commanding it, loading the main gun, and firing that main gun. A well-armored, big gunned, fast tank, which is easy to maintain isn't worth all that much if the crew finds it hard to operate.

Maybe the steering is really hard, maybe the driver's visibility sucks. Maybe the gun has a tendency to injure the guys loading and firing it. Maybe the commander has to do more than command the tank. (Here I'm thinking of some of the early tanks in WWII where the commander had to load, aim, and fire the gun, while also telling the driver where to go.) Not good. Maybe the commander can't see squat when his hatch is closed, which is often necessary when enemy infantry is about, nothing they like better than shooting tank commanders!

Another thing about usability is how easy is it to get out of the tank when the crew has experienced what Major Moran likes to call the "significant emotional event" of having the skin of one's tank pierced by an enemy projectile. In other words, "Oh my God, the tank is on fire!" Important for crew morale, believe me!

Let's have Major Moran cover that for a few WWII tanks -

Yeah, if you can't get out of a burning tank, you know it, you've seen it happen to other crews...

You might be a bit reluctant to be a tanker, the infantry is looking better and better. (Or you could have joined the Air Force!)

In many respects, in fact in most respects, the M4 Sherman was a very good tank. Credit where credit is due and damn it, it got the job done. (Hell, even the Soviets loved 'em!)

Anyhoo, that's what I look for in a tank. You may have other criteria, which I hope you'll contribute in the comments. To wrap up, here's an interesting video of someone's "top ten" tanks of World War II. Yes, they left some out, everyone discounts the French tanks, some of them were very good, better than what the Germans had for that matter. Thing is, their pre-war doctrine (the way one uses a tank) sucked and while they were fixing that...

Hey, here come the Germans.

And yes, the computer voice in the video is very annoying at times, there are a couple of errors as well (can you spot them?), but hey, tanks!

Your turn.