N-L-M

Also that story is purely indicative of what everyone in the RtBA community has been seeing and saying for years. Just before we had instant communication with millions of people 24/7 via an affordable pocket device, we were called names. Crazy, paranoid, psychotic, you name it. It was just a few years ago that yet another mental health bill was knocked down that was really just a backdoor gun control measure. 
 
We've been called mentally deranged for YEARS by the left, all for pointing out the very obvious narrative that they've been trying to push for the past three to four decades.
 
And the craziest part is that the argument has literally never changed. It's the exact same tired talking points that they started with in the 70s and 80s. They got the GCA68 passed and smelled blood in the water. 
 
Since then it's been a constant fight, with "debates" barely measuring up to what I've seen in high school debate clubs. 
 
It's always clueless people trying to fool or scare an ignorant majority into giving rights away. And anytime an argument is made, it gets batted around with ad hominems and strawmen are set on fire. 
 
The left had one hell of a chance with Obama. But amazingly, he was too lazy or spineless to go after guns. He made damning speeches that really portrayed how little the left thinks of the average American in fly over states ("it's easier for a student to buy a Glock than a book!").
 
But he never actually did anything. Pathetic. 
 
So yes, everyone is tired. All the facts and data and logic are on the side of rights activists. Emotionally pleas are the only thing the left has, so it trots out crocodile tears and children every chance they get to sway public opinion. They are creating talk shows and news programs that deliberately attempt to erode conservative ideals that are shared by a majority of people in this country ("you don't really believe in X, do you? Only dummies believe in X. It's just common sense that Y is right. Now here's a thinly veiled insult disguised as a joke and a word from our sponsors, pharmaceutical industry C and coke product D").
 
I am grateful that independent sources are so easily obtainable these days. That is, until the internet is 100 percent owned by the left. Looking at their contributions to Google, they are trying to buy their way into that now. 

Since we've got an arms race, my tank has been showly shifting more and more towards Not An M41.  Going to improve the suspension.  Gave it a meaner gun and a better shaped turret, but made sure to keep all the comfort.  Turret's gotten pretty fat, may be able to trim some off the back half still.
 

 
On second thought, it's entirely possible that I've also just got the turret itself at too large of a scale
 

By their powers combined:

Since I'm in the mood, a little bit of commentary about the process I went through designing these tanks, and, critically, to explain why there are four instead of just two.
 
Development started with what I always thought of as the "Main Battle Tank" requirement. Given the time period, and since the Baberams/Caracal was an all-welded design that was pretty straightforward to model in SolidWorks, I decided to challenge myself with the Donward and design an all-cast tank. My initial approach to this was satisfactory but... Problematic. I designed the XM12 essentially the same way I had the Baberams, and based many of its features on some of my previous concepts for design competition entrants, as well as the T95 Medium, M103, Chieftain, M48, and Centurion (hence the very "western" look). I emphasized comfort in the design (perhaps a bit too much), and insisted on -10 degrees of gun depression with a 140mm gun, a standing loader, and a centerline driver. Regarding the gun, I wanted to arm it with a rifled gun optimized for APCR ammunition, but knowing that APDS and fin would be on their way before too long I wanted to give the turret as much upgrade potential as possible. The gun I came up with was an 85mm with a round that was initially based on the 7.5cm KwK 42 case, but over time the base expanded slightly to about the same as the 90mm M3. This resulted in the 85x640R which arms the Sandy E4 and E6. To ensure that the Donward would be fully designed for a modern 140mm gun, I made the breech and recoil stroke equivalent to something in that range, and designed the turret around that. As part of an "arms race" between myself and @N-L-M, I developed additional 120mm and 152mm high velocity guns.
 
To achieve the "cast" look, I ended up extensively using the fillet tool, which created a convincing enough model. However, the model itself was by the end essentially a collection of some hundred and forty-five fillets, which made the model a little unstable and extremely difficult to modify.
 
'
 
 
^This sucks
 
This made things much more difficult when, in discussions with @N-L-M it became apparent that while protection was excellent to the point of ludicrous at the 0 degree angle, protection dropped off as the turret turned to the side. Also, the turret had some conspicuous weaker spots near the turret ring that concerned me.
 
The hull was broadly based on a Centurion, but with an elliptical glacis, since I wanted to figure out how to model one of those. The glacis on the resulting Donward is slightly elliptical, but it probably could have been flat for the same effect. With the hull and turret broadly modeled, I finally decided to take a look at the actual requirements presented in the OP. I discovered that I was barely skating by on width, and that my 50t design weight guideline was five tonnes heavier than the maximum listed in the solicitation. So pro, Nathaniel, so pro. Fortunately, the Donward was a bit under 50t to begin with, and so I was able to reduce the side armor on the hull and make a few optimizations to the turret and bring my curb weight under 45 tonnes. However, the margin I had planned into the design for additional armor and guns was pretty much eaten up by this, which added to my overall dissatisfaction with it.
 
Despite the issues with the turret and the weight, I wrapped up design of the Donward almost all the way, and moved on to the light tank.
 
I made some assumptions when designing the Sandy that caused significant difficulty in its design, as well. The first was that I would be able to use the same suspension elements from the Donward and come in under the width limit, and the second was a self-imposed weight limit of ten tonnes. Using a cleft turret and lightweight aluminum construction it seemed like the Sandy would be about 7 tonnes initially, but once all the other elements were added it quickly ballooned to well above 10. This created a dilemma for me regarding the goal of the Sandy, and I explored a handful of other turrets which would bring the Sandy into a class more similar to the T92 or M24. I developed two more heavily armored turrets, one welded one cast. The cast turret was obviously better armored and more lighter, so I decided to continue work with it. Once I began exploring powerplants, however, it became obvious that the idea of turning the Sandy into a "medilite" was not going to work. The Sandy's hull was designed to accommodate a ~300 hp engine, and stuffing in a powerplant that could give a 20 t vehicle more than 20 hp/tonne didn't really seem feasible at the time. It was at this time I decided to redesign the hull.
 
The first change I decided to make was to change from aluminum to steel, and add armor. Along with that, I moved the engine compartment from the front left alongside the driver to the rear like a normal, sensible tank. I figured that with these changes the tank would come in well over 20 tons and plucked a goal weight of 35 tonnes out of thin air. I figured I would use the elliptical turret I had developed for the new, um, whatever tank. At some point during this process I realized I was basically making a T-55 with more gun depression and decided to embrace this by picking the codename "Roach", however this decision came fairly late to the point that most of the Roach parts and assemblies still reside in the Sandy subfolder. The Roach retained the 5 degree glacis angle of the Sandy, but little else, having essentially a completely new hull, and - eventually - a new turret, too. Shortly after the development of the Roach began, I started to second guess my choice of armament. The 85mm was a potent gun, but its reliance on APCR rather than full caliber shot was something that concerned me. Initially, I bored out the 85mm gun to a 100x640R round, but was quickly caught by the allure of a D-10T analogue. I found that I could do this with a 100x685R round using a wider case base, which resulted in the current 100mm gun that I chose as the final main armament for both the Donward and Roach. Since the Roach was designed for an intermediate 600 hp powerplant, it was quickly converging on the historical T-55.
 
Upon completion of the first hull assemblies, I discovered that the Roach - like the Sandy - was far too wide to meet the 10.8 foot specification. Discussions with @N-L-M indicated that the Roach's suspension - inherited from the Donward - could use significant optimization. Specifically, I found that the roadwheel arms and spring mount assemblies were designed to properly space against a 20 degree hull angle - while the Roach had sides set at 0 degrees. A program of re-dimensioning and compressing the suspension across the x-axis began, which resulted in a much more compact vehicle in the x-dimension, after which design progressed fairly smoothly. It was this development that proved to be a watershed moment for the Sandy.
 
The suspension elements developed for the Roach added the promise of finally reigning in the Sandy's always-excessive width. Using these parts, 16" wide tracks (instead of 21" like the Roach and Donward) and with some additional re-dimensioning, the Sandy was finally brought within the 10.8 foot limit, without compromising the already-strapped internal hull volume. It was at this point that I re-married the hull and original cleft turret, and found a reasonable curb weight of less than 13 tonnes - more than I'd wanted at first, but still plausibly air-droppable from an aircraft of the given technology level. The original concept of the Sandy, abandoned days prior, was back.
 
At the same time, my satisfaction with the Roach's elliptical turret design was low. The turret was a simple construction of a number of revolve and revolve-cut features, which presented some pretty flat angles across the frontal arc, potentially making it more vulnerable to APCR than I'd like. Complex geometry like lofts and boundary features had always been a major problem for me in SolidWorks, but I was going to have to bend them to my will to make a better frying pan turret. After an entire day of struggling with features that didn't want to behave right, I finally ended up with an improved frying pan with the major shape produced though a single boundary feature.
 


 
Elliptical turrets, old (top) vs new (bottom). The boundary tool was crucial to producing improved turret geometry.
 
Comparing the protection of the old and new turrets re-emphasized the poor optimization of the early elliptical design, but this could be fixed fairly easily while making the model simpler, which resulted in a third, "lightweight" design:
 

 
The multiple revolve-cuts about different axes of the old turret were replaced with a single carefully dimensioned revolve-cut that produced a continuous transition from the thicker frontal armor to the thinner rear armor, and which didn't leave any thin spots towards the top of the turret, as had been present in the old version. This new version was also some 550kg lighter than the first elliptical turret, which made it a suitable candidate for a new version of the Sandy, which could fill the roll of a sub-20 t light tank for desert campaigns. It was pointed out by @N-L-M that the rubber band tracks of the Sandy would be more resistant to damage from sand and dust than linked metal tracks, provided the weight of the tank didn't exceed a certain threshold. The light version of the elliptical turret would also provide plenty of protection against threats from Deseret, even though its angles were not as extreme as the improved turret. The addition of the 20mm coaxial gun from the Donward and Roach would give the tank plenty of ways to kill light Deseret vehicles, as well. A larger displacement engine equivalent to the DD 6V92T would be a tight fit in the Sandy hull, but would give the tank 25 hp/tonne, which is about what I was shooting for. This version became the XM13E6.
 
I've skipped over a number of things, such as the numerous variations of cupola and commander's hatch I tried before settling on the current M103-inspired one, and the various armor packages and styles I tried out with the Donward turret, but this should give people some idea of what my process was like.

Alright, at long last I think I have finally finished. Or, at least
 

 
I am going to post up some basic data from my worksheets, writeups to follow later.
 

 
XM12 Donward Main Battle Tank
 
Crew: 4
Curb weight: 43.1 t
Gross weight: 45.3 t
 
Armament:
100x685R L/52 rifled gun firing APCBC, HE, and APCR
53 rounds capacity, +25/-10 elevation
20x140mm coaxial autocannon firing APHE, HEI, and APDS
7.62mm M240 coaxial machine gun
.50 caliber M2 machine gun
7.62mm coaxial machine gun
 
Hull armor:
Upper glacis - 4.4" at 28 degrees - 239mm LOS (slightly elliptical)
Lower glacis - 3" at 44.6 degrees - 108mm LOS
Side - 2" at 15 degrees, plus 1"side skirts - 78.4mm LOS (spaced)

Turret armor:
0 degree: 512mm at forehead, 240mm at nose, 186mm above ring
15 degrees: 502mm at forehead, 220mm at nose, 167mm above ring, 339mm sides
30 degrees: 358mm at forehead, 200mm at nose, 147mm above ring, 175mm sides
45 degrees: 262mm at forehead, 154mm at nose, 136mm above ring, 124mm sides
 
Powerplant:
750 hp air-cooled turbocharged V12 diesel, 29.4 L displacement, cross-drive transmission
16.6 hp/t
 
 
 

 
XM13E4 Sandy Airdroppable Reconnaissance Vehicle
 
Crew: 3
Curb weight: 12.9 t
Gross weight: 13.9 t
 
Armament:
85x640mmR rifled gun firing APCBC, HE, and APCR
34 rounds capacity, +25/-5 elevation
.50 caliber M2 machine gun
7.62mm coaxial machine gun
 
Hull armor:
Upper glacis - 20mm at 5 degrees, 35mm at 35 degrees (aluminum)
Lower glacis - 35mm at 33.5 degrees (aluminum
Side - 10mm all around (aluminum)
 
Turret armor
1" thick cupola walls (steel)
 
Powerplant:
305 hp turbocharged water-cooled V6 diesel, 7 L displacement, cross-drive hydrokinetic transmission
22.0 hp/t
 
 
 

 
XM13E6 Sandy Light Reconnaissance Vehicle
 
Crew: 4
Curb weight: 17.7 t
Gross weight: 18.6 t
 
Armament:
85x640mmR rifled gun firing APCBC, HE, and APCR
34 rounds capacity, +25/-10 elevation (-5 over tracks)
20x140mm coaxial autocannon firing APHE, HEI, and APDS
7.62mm M240 coaxial machine gun
.50 caliber M2 machine gun
7.62mm coaxial machine gun
 
Hull armor:
Upper glacis - 20mm at 5 degrees, 35mm at 35 degrees (aluminum)
Lower glacis - 35mm at 33.5 degrees (aluminum
Side - 10mm all around (aluminum)

Turret armor:
0 degree: 211mm at base to 248mm at top of gun shield, 244mm at roof
15 degrees: 209mm at base to 245mm at top of gun shield, 241mm at roof
30 degrees: 201mm at base to 238mm at top of gun shield, 234mm at roof
45 degrees: 190mm at base to 226mm at top of gun shield, 221mm at roof
60 degrees: 174mm at base to 210mm at top of gun shield, 205mm at roof
 
Powerplant:
475 hp turbocharged water-cooled V6 diesel, 9 L displacement, cross-drive hydrokinetic transmission
25.5 hp/t
 
 
 

 
XM15 Roach Medium Tank
 
Crew: 4
Curb weight: 36.0 t
Gross weight: 37.8 t
 
Armament:
100x685R L/52 rifled gun firing APCBC, HE, and APCR
45 rounds capacity, +25/-9 elevation
20x140mm coaxial autocannon firing APHE, HEI, and APDS
7.62mm M240 coaxial machine gun
.50 caliber M2 machine gun
7.62mm coaxial machine gun
 
Hull armor:
Upper glacis - 55mm at 5 degrees - 631mm LOS
Lower glacis - 125mm at 45 degrees - 177mm LOS
Side - 80mm at 0 degrees
 
Turret armor:
0 degree: 225mm at base, 225mm at top of gun shield, 225mm at roof
15 degrees: 227mm at base, 212mm at top of gun shield, 217mm at roof
30 degrees: 234mm at base, 197mm at top of gun shield, 211mm at roof
45 degrees: 235mm at base, 191mm at top of gun shield, 198mm at roof
60 degrees: 223mm at base, 187mm at top of gun shield, 191mm at roof
 
Powerplant:
620 hp liquid-cooled V12 diesel, 38 L displacement, cross-drive transmission
16.4 hp/t

As I find myself in a bit of a time crunch, the light tank proposal will be quite a bit less fancy than the Norman.
The preliminary sketch is as follows:

8x8 or 6x6 wheeled deathtrap, with double wishbone steerable suspension on the first and fourth axles (if present), modified Christie on the second and third.
Armament is to be a low-pressure 90mm feeding from a 6-10 round autoloader (as a ready rack, with spare ammo) or a dual-feed 30mm modeled after the 2A42. A coax 7.62 is fitted in any case. Due to weight and volume considerations the 30mm turret is liable to come with more goodies than the 90. 30mm APDS and later APFSDS will kill any light vehicle which would theoretically be developed in the next few decades, while 90mm HEAT will be capable of killing heavy armor. 90mm HE will also be useful for fire support.
There is an additional armament component which will be expanded on later.
Proposed variants of this design are light/scout tank, FSV, APC (Saracen-style), SPAA and supply vehicle for now.
The hull, turret, and some fittings will be modeled when I have the time; note that this is a preliminary sketch, nothing more.

looks a bit familiar....

For some unknown reason the renderer crapped out on me so I had to change the coloring on the Norman.
Anyhow, short of vents and rough shapes of equipment in the engine bay, the Norman is DONE. Some details are stand-ins for things I don't have the time to model properly; for example, the loader's MG should be on a skate ring, not a pintle, and the commander's MG is supposed to have linkages for elevation and firing (enabling its use under armor, Abrams-style). Also the bustle stowage rack is not modelled.
I may not have time to properly model a light tank, which means I might have a low-visuals submission for that part.
Full writeup will come later, when I again have time.

By the way, if anyone's wondering, the frontal turret spaced armor isn't a shot trap, as it's the same thickness as the hull roof underneath it, and therefore anything capable of penetrating the roof after bouncing will penetrate the spaced armor, not bounce.

Necro-threading a bit, but I'd rather not start a new thread.
https://news.usni.org/2018/08/28/navys-next-large-surface-combatant-will-draw-ddg-51-ddg-1000-dont-call-destroyer
The USN, despite its failed development programs, needs new ships as older ones (Ticos) wear out, and to increase fleet numbers to the desired 355. As the Zums were cancelled, and replaced in procurement by the ABIII, This still leaves a need for Tico replacements. And as the ABIII pretty much maxes out what the AB hull can do (unless you want to extend the hull with a plug, which is possible and even increases fuel economy thanks to better fineness ratio), A new bigger hull is needed. I note that other than some command facilities, a tail, and larger VLS capacity there isn't really all that much different between the flt IIA Burke and the Ticos. So it's possible that the next ship will be a "main battle ship", as it were, replacing both the Ticos and older Burkes.
I currently don't have the time but I fully intend to return to this thread for an effortpost about large and small surface combatants and what I see as being their roles, requirements, and uses in both war and peacekeeping.

So everyone should do up so marketing material, and then come up with a plan for how you would bribe the proper officials to consider the merits of your design more carefully. What is the hooker and blow situation in 2239?

Boeing won the MQ-25a competition.
https://news.usni.org/2018/08/30/navy-picks-boeing-build-mq-25a-stingray-carrier-based-drone

I don't think the microfighter concept is a strong one with current technology.  I also think that fighters designed by small countries are at a very large disadvantage because of the current state of engine technology.  This wasn't always the case, but it is the case now.  Sweden made fighters that were perfectly competitive with those of the USA and USSR throughout the Cold War, and during WWII small nations like Romania and Australia managed to turn out fighters that were perfectly competitive with those of major powers, at least for a time.

I should clarify that I mean "small" in the sense of economic power, not land area.  The UK and Japan could both turn out decent fifth-generation fighters in the near future if they decided it was a priority (UK more easily than Japan).  

The main problem is that state-of-the-art jet engines can only be made by a handful of companies.  Only those companies have the experience and expertise to design and produce the high temperature components of a top-of-the-line jet engine.  John Golan's Lavi book explains that the Israelis were confident that they could produce every single component of the Lavi except the engines.  The Lavi was not low-tech, far from it.  The entire fuselage was to be filled with Digital Radio Frequency Memory (DRFM) jamming devices, the nose would contain a look-down-shoot-down radar, and the wings would be made of aeroelastically tailored carbon fiber composites.  All of this stuff was comparably advanced to anything the US or Soviets had airborne at the time, and in some cases (notably the wing composite structure and jammers) it was better.  But they categorically could not make the engines in Israel.  In fact, any license-production of the engines would amount to mere assembly of knock-down kits of engine components.
 
In order for a jet engine to have better efficiency and power density, the core inside the engine needs to experience greater temperature gradients:



The Y axis is pressure and the X axis is volume.  Pressure multiplied by volume is work, so the entire area enclosed by the diagram is the work the engine produces.

Since a gas increases in temperature when it is compressed, improving engine performance necessarily entails the use of materials that can withstand greater temperatures.  Current top of the line gas turbine blades are made of mono-crystal nickel alloys, and those are a stone cold bitch to make.  Only a handful of companies worldwide can do it. 
 

 
But these exotic, difficult materials aren't just a luxury.  They're fundamental to achieving a high performance thermodynamic cycle.  A jet engine can certainly be made that doesn't use these exotic nickel alloys, but they're bigger, heavier and less efficient than one that does.  Check out this comparison of a GE F404 with a GE J79:



The earliest versions of F404 produced nearly as much thrust as the last versions of the J79, and later versions eclipsed it entirely, all while being narrower, much shorter, slightly more fuel efficient, and requiring enormously less maintenance.  Mono-crystal nickel alloy blades are the sine qua non of modern jet fighter engines.
 
Off the top of my head, there's one company in the UK that can make these things, two in the USA, one in France, two in Russia and one in China, but they're still getting their feet under them.  The Japanese have enough expertise in industrial turbines and exotic materials science that I think they could figure it out if they threw a huge wad of money at the problem.  India is trying to develop independent expertise, but... it's Indian defense.

This means that any country that wants to develop a new fighter that is not on the list above has to make do with engines from a country that is on the list above.  This means that a lot of the fundamental decisions about the aircraft are made for them.  At what altitude and airspeed will the fighter be most efficient?  A small country that can't design engines has to choose from a handful of already available engines and hope that the parameters of the existing designs closely match what they want.
 
There is also the possibility that the small country doesn't get the engine they want at all.  SAAB is stuck with a weaker version of the General Electric F414 for the Gripen E/F that only produces 98 kN.  Since the Gripen E/F is quite a bit heavier than earlier versions, this leaves it somewhat underpowered.  General Electric had calculated that, with enough development money, they could develop a souped-up variant of the F414 capable of producing 120 kN of thrust.  They pitched this idea, called the F414 EPE, to the US Navy as an upgrade for F/E/A-18E/F/G-e-i-e-i-o fighters.  The US Navy was initially interested, but ultimately decided to spend the money elsewhere.  So SAAB is stuck with an underpowered Gripen E/F and can't do anything about it, as they're not really in a position to spend the megabucks that GE will want for engine development.
 
Another problem is that the current air warfare paradigm doesn't really favor small fighters.  I wrote a post about the effects of scaling on fighter performance on another forum, so I'll copy-paste it here:

 
 
From simple physical scaling effects, smaller fighters should have an edge in maneuverability but should be at a disadvantage in terms of range and speed.  With the fifth generation of fighter jets emphasizing supercruise capability and long range (in order to help compensate for small fleet sizes), a relatively small fighter is not looking like a great trade-off.  There are other problems with micro-fighters under the current fifth-generation paradigm.  Radar performance (range, resolution) is directly related to the size of the antenna.  Bigger fighters can support a larger radar.  Internal weapons bays are more or less a must for stealth, and a small fighter is going to have a much harder time supporting internal bay that can carry all the sorts of ordnance it might need to carry.

The hybrid light strike/trainer concept has more merit, but I am not sure that this idea is a wise allocation of resources.  Combat aircraft designers have moved towards multi-role designs that double as fighters and as attack aircraft because individual aircraft have become more expensive and because mission electronics have become so much better.  But aerodynamically speaking, a multi-role aircraft is not an attractive idea.  In order to have the requisite agility needed for air to air combat, fighters need to have lots of features that compromise their efficiency.  Fighters have huge wings, proportionally speaking, so that they can produce lots of lift.  They have vortex generators like canards, dogteeth and LERXs to allow them to pitch to very high angles of attack.  They have gigantic vertical stabilizers, ventral fins and other auxiliary and oversize control surfaces to maintain control while they are performing extreme maneuvers.  All of this stuff improves agility, but adds weight and drag.  A light strike aircraft that doubles as an advanced trainer might be able to perform useful missions in a strike role (as the L39 albatross is today in Syria), but it won't do very much in an air-to-air role.  If, in any realistic war, it would just be killed in any sort of contested airspace, it makes more sense to stop pretending that it can double as some sort of fighter, and get rid of all of the features that make it more agile, and just use it as a light bomber.  Better still, make it a drone.
 
I think that is the balance of considerations based on modern technology.  Changes in technology could change this balance a lot.  For instance, General Electric is working on silicon carbide turbine blades, since mono-crystal nickel alloy blades are nearing the limits of their potential.  Once the silicon carbide technology is mature, it might turn out to be much easier to produce than the mono-crystal nickel alloys.  It is also possible that computers and CFD software will improve to the point where institutional experience in engine design matter less, and small nations will be able to reasonably design and produce their own fighter jet engines.  But that is speculative.  For right now, I think fighter aircraft are really only competitive if they're fairly big, and if they come from fairly big nations.

I hope you like submarines.
 
http://www.dtic.mil/dtic/tr/fulltext/u2/a059747.pdf
The submarine equivalent to Technology Of Tanks. By the chief engineer at Kiel when Germany restarted production. I know a few mechanical engineers involved in subs who say that this is about as good as books on the subject get.
 
http://www.dtic.mil/dtic/tr/fulltext/u2/342338.pdf
Unconventional sub propulsion methods.
 
http://www.dtic.mil/dtic/tr/fulltext/u2/a213542.pdf
Submarine electric propulsion
 
http://www.dtic.mil/dtic/tr/fulltext/u2/a538633.pdf
AIP

I hope you like submarines.
 
http://www.dtic.mil/dtic/tr/fulltext/u2/a059747.pdf
The submarine equivalent to Technology Of Tanks. By the chief engineer at Kiel when Germany restarted production. I know a few mechanical engineers involved in subs who say that this is about as good as books on the subject get.
 
http://www.dtic.mil/dtic/tr/fulltext/u2/342338.pdf
Unconventional sub propulsion methods.
 
http://www.dtic.mil/dtic/tr/fulltext/u2/a213542.pdf
Submarine electric propulsion
 
http://www.dtic.mil/dtic/tr/fulltext/u2/a538633.pdf
AIP

Single-pin tracks are much harder to break by torsional forces on the track, thanks to the large number and size of points where the pin is subjected to shear forces under such a loading.

Double-pin tracks are easier to break by loading like this as they only have the center guide connector and end connectors.

That in my opinion is the case. I Don't have any hard evidence to back it up right now.
This is also in my opinion why single-pin tracks are preferred for hard, broken ground where the track is liable to ride on large rocks unevenly, applying torsion to the track.

The 64 has narrower knife wheels, which remained intact and effectively 'cut' the track. The 219 has wider wheels, the outer one of which got wrecked. The wider wheels support the track more against uneven loading, and the energy spent on breaking the wheel prevented it from breaking the track.
 
Again, this is just informed conjecture.

Command guidance is out of the question at least for the terminal phase, you cannot get the required accuracy- your accuracy is limited by the accuracy of the fire control radar, which has both range estimation errors the the target and interceptor, and time delay (long pulses for good gain at range and things)
Lower quality standards may account for it, but Sidwinders, AMRAAMs and ESSMs are also mass produced. Just how much did RAFAEL throw QC into the trash to literally make a missile an order of magnitude cheaper?
Or are Sidewinders just not that expensive? 
Having just gone through GIS, I note the following: the opaque ogive on the Tamir is split into half clamshell-style, and it looks like the halves can separate to expose the seeker.

If so that'd mean that when switching to terminal the seeker head gets exposed, but until then it's not, which keeps it cool. This would allow the use of uncooled IR seekers, which are indeed much cheaper.
Combined with the peripheral IR, this could also solve the odd engagement geometry fuzing problem critics like to harp on about.

Like the seekers in the Spike-SR, which is cheaper than Javelin. With a terminal engagement range of 1-2km, that's good enough.
That nose seeker is either a small uncooled IR head or a very small simple SARH reciever. And I'm currently tending towards the first.

German concept proposed during the Kampfpanzer 3 / FMBT project to the UK via https://andrei-bt.livejournal.com/928203.html
 
Twin-gun casemat tank from Maschinenbau Kiel:



 
Low-profile turret tank with driver in turret by Krauss-Maffei (similar to MBT-70, but with 120 mm smoothbore gun and manual loader - maybe derived from the Eber concept):


 
Data:


 
Armor is spaced steel plates, sometimes with fuel inbetween them. The MaK design has 727 mm thick armor, but the actual steel thickness is just 259 mm...




 
Note that according to Krapke a third concept (AFAIK either turretless or with unmanned turret?) was proposed.

Command guidance is out of the question at least for the terminal phase, you cannot get the required accuracy- your accuracy is limited by the accuracy of the fire control radar, which has both range estimation errors the the target and interceptor, and time delay (long pulses for good gain at range and things)
Lower quality standards may account for it, but Sidwinders, AMRAAMs and ESSMs are also mass produced. Just how much did RAFAEL throw QC into the trash to literally make a missile an order of magnitude cheaper?
Or are Sidewinders just not that expensive? 
Having just gone through GIS, I note the following: the opaque ogive on the Tamir is split into half clamshell-style, and it looks like the halves can separate to expose the seeker.

If so that'd mean that when switching to terminal the seeker head gets exposed, but until then it's not, which keeps it cool. This would allow the use of uncooled IR seekers, which are indeed much cheaper.
Combined with the peripheral IR, this could also solve the odd engagement geometry fuzing problem critics like to harp on about.

Like the seekers in the Spike-SR, which is cheaper than Javelin. With a terminal engagement range of 1-2km, that's good enough.
That nose seeker is either a small uncooled IR head or a very small simple SARH reciever. And I'm currently tending towards the first.

https://www.cia.gov/library/readingroom/docs/DOC_0000498195.pdf
CIA T-72 breakdown, includes loads of details

https://www.cia.gov/library/readingroom/docs/DOC_0000498195.pdf
CIA T-72 breakdown, includes loads of details

nice, but seems to have limited coverage.
In other news:

>hull armor improved
>Hull spaced armor added
>sideskirts added
>Sponson boxes added
>slight experimentation with the sand colors.
The 145mm gun is still in because it's the worst-case for sponson clearance.
Like the turret, the hull spaced armor contains stowage space. The frontal slope would probably be used for stowage of tools, or alternatively layers of glass textolite. The other boxes will be described at some length later. All can of course be fitted with ERA when ready, and the all the thick plates are high-hardness for the shattering effect.

nice, but seems to have limited coverage.
In other news:

>hull armor improved
>Hull spaced armor added
>sideskirts added
>Sponson boxes added
>slight experimentation with the sand colors.
The 145mm gun is still in because it's the worst-case for sponson clearance.
Like the turret, the hull spaced armor contains stowage space. The frontal slope would probably be used for stowage of tools, or alternatively layers of glass textolite. The other boxes will be described at some length later. All can of course be fitted with ERA when ready, and the all the thick plates are high-hardness for the shattering effect.

The turret now sports spaced high-hardness armor to shatter those pesky ultra-high velocity APCR rounds our engineers are convinced will be all the rage in the near future.
These are bolted and easily replaceable with, say, ERA arrays when it becomes available. The internal pockets have roof doors and are intended to hold small-arms ammo or ration boxes.

Driver's hatch is now a thing:

Turret had to be slightly raised and enlarged to ensure the gun clears the hatch and periscopes at full depression.
For those wondering, yes the driver is mildly supine. I didn't model an IR-capable hatch because I'm lazy and didn't want to make yet another component so I just used the standard periscopes.
This swinging hatch design with the periscopes mounted  is inspired by the Leclerc and Leopard 2. The problem with it is that the resulting access hole is smaller than the hatch dimensions would suggest, as the periscopes must remain within the hull. For early IR, which is much larger than natural-light periscopes, the solution is to have the driver dismount the scope before opening the hatch. The IR periscope needs a rotating mount as there's only one, with a limited FoV.
but maybe that can be handwaved as the head being the same as the daylight periscope and therefore fitting in the same well.
Clearance illustrated:

The commander has some, if limited, vision over the GPS even at full depression, allowing H-K operation. The cupola is fitted with commander's traverse and elevation override, with slew-to-cue.
I'm really liking how this is shaping up.

EDIT: current weight, including hull, turret, gun, extras, final drives (modeled as part of the hull for now) tracks and suspension come out at 30 tons.
To do this some densities were rectally extracted (wheel hubs include ball bearings and quite a bit of air, I approximated it as half empty, likewise most of the volume of the wheels are rubber)
So assuming suspension is 8-10%, tracks 8--10%, armor 50%, and the gun 5-7%, this means I've got around 70%-75% of the weight accounted for. This in turn leads me to a final weight of around 40-42 tons. Good.

The tank now also has a name:
XM-2239 "Norman"
Named for General Stormin' "did you hear he died" Norman Schwarzkopf.

Random fun fact: the Soviets did some testing of the Kh-80 on a converted Yankee class sub


 
I believe it was that one (K-420, aka Yankee Sidecar)