couple Q's for the treadheads--ON TOPIC, I promise!

A main battle tank (also called a medium tank) is a balanced design that has enough firepower for most battlefield tasks, enough armor protection to survive most hits, and enough mobility to be strategically useful. It is ordinarily a fully tracked armored vehicle with a fully rotating turret. If you compromise mobility and/or armor protection or delete the turret in favor of higher firepower, the vehicle is usually considered a tank destroyer (on the other hand, if you increase both armor and firepower at the expense of mobility, you have a heavy tank). Any vehicle that carries a gun but lacks any of the attributes of a tank is a self-propelled gun. It may have little armor or no armor at all, even though it may have a turret. SP guns are ordinarily used in the indirect fire role. Self-propelled guns that are armored like tanks and are used in a direct fire role are termed assault guns (from the German Sturmgeschutz). During WW2, US TD's were essentially stripped-down tanks with slightly oversized guns but armor only sufficient to stop rifle bullets. They were supposed to use "scoot and shoot" tactics, as they could not survive any kind of hit from an enemy tank. If used in place of tanks in an assault role, they would suffer heavy casualties. German tank destroyers were of two varieties--the early Panzerjager were mostly recycled light tanks with their turrets replaced with high velocity antitank guns surrounded with thin gunshields. They were at a severe disadvantage in any role other than ambush. The later Jagdpanzer designs were armored like tanks, but lacked a rotating turret, so all were technically assault guns. They weren't as bad off as the Panzerjager, but they were at a severe disadvantage in offensive ops, as they could not fire to their flanks. Today the role of tank destroyer is handed off to light wheeled or tracked vehicles equipped with guided missiles. "Bogey" is a term borrowed from railroad technology before World War Two. The box containing the springs and axles is a bogey unit, and the term was applied to the external vertical volute spring suspension units used on Lee/Grant/Sherman and Stuart tanks, so the road wheels were sometimes called bogey wheels, or bogies for short. The term came to be applied even to vehicles that had torsion bar suspensions. Likewise, the tracks were often called "treads," though strictly speaking the tread would be that part of the track shoe that actually contacts the ground. These terms are rarely heard today, however. As for what's essential in designing a tracked suspension, it depends on how much weight the suspension has to support. J. Walter Christie's early high speed suspension systems from the 1920's used very few wheels, but his vehicles didn't weigh much. Some vehicles like the Stuart tank, had the idler wheel double as a road wheel, but designers usually don't want the drive sprocket to carry weight, as it will put lateral stress on the final drive gearbox. Figure on at least two road wheels besides the driver and idler. If the track has to cover a long distance without a wheel to support it, you run the risk of snapping it outright. For the moon, you might be able to cheat a bit. Some arctic vehicles don't use road wheels at all--the track actually slides along a stainless steel skid on the bottom of the external bogey unit. If you want some ideas, check out Fred Crismon's "US Military Tracked Vehicles." It surveys a couple of thousand tracked vehicles from WW1 to

1991, including those snow vehicles I mentioned. Gerald Owens

Ok, call me naive, but... 1. What defines a 'tank' versus a tank destroyer, or, more importantly, an SPG? I always figured anything with treads and a B.A.G (Big A$$ Gun) qualified as a tank. 2. Define bogeys versus roadwheels, and why do some use one, some the other? Ok, three is more than a couple, but I'm on a roll, so... 3. What are the prereqs for a treaded vehicle, ie what wheels, besides a driver and an idler, are absolutely essential? That question arises from my desire to build a treaded something for lunar or other-worldly use, and I was looking at multi-track assemblies, like one on each corner of the vehicle as opposed to one full length on each side. Thanks.

Alrighty then....Thank you both very much. The wife and I were at the Butch O'Hare show near Chicago over the weekend and I saw some German vehicles that were rather confusing, ie 'tanks' with no turrets. I have seen them before at other shows, but not being an armor builder and therefore not really caring, I didn't give it a lot of thought. But I've come to a bit of an impasse of late, not really knowing whether I was again losing interest in the hobby, or just my normal subjects (aircraft), and have considered a change. I thought a few good 'what-ifs' and 'why-nots' might be in order, such as "what would a lunar tank look like?". And here I am. Again, thanks.

Depends on the country and era. In the WW II US Army a tank destroyer was a vehicle designed to destroy tanks, regardless of layout. Early US TDs were nothing more than an anti-tank gun mounted on a small truck. These evolved into self-propelled guns or, in the vernacular, Gun Motor Carriages. These were based on existing tank chassis with a thinly armored, roofless turret, and so generally look like a tank. TD development was under the control of the Tank Destroyer Corps, not the same folks responsible for tank development so lots of politics. Although the vehicles performed well, the concept was dead-end and abandoned by the US after WW II. Steve Zaloga has authored several inexpensive books over the last few years on the subject. Fascinating reads. Other countries' developments tended to be fixed superstructures on tank chassis with a larger gun than the tank could carry.

curt

The term "main battle tank" was coined by the Soviets in the early

1960s to cover their new family of tanks beginning with the T-64. They termed it that as it replaced the "Medium" tank (then any tank between 25 and 40 tons) and "Heavy" tanks (40 and up) as it had the armor of a heavy, the gun of a heavy, the mobility of a medium and weighed (originally) only 36 metric tons.

Incidentally the Swedes are the only ones I know of to ever have a turretless tank (the S-tank) and a turreted tank destroyer in service at the same time. Go figure.

Cookie Sewell

"Disco58" wrote

A tank is a heavily armored, full-tracked, combat vehicle with a direct fire weapon in a rotating turret that is meant to close with and defeat enemy tanks and other ground forces.

KL