Mother of all Infantry Support Vehicles!
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And a modern variant.
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An
assault gun is a gun or howitzer mounted on a motor vehicle or armoured chassis, designed for use in the
direct fire role in support of infantry when attacking other infantry or fortified positions. The term is a literal translation of the German word
Sturmgeschütz. Nazi Germany introduced the first purpose-built assault gun, the StuG III, in 1940, thus establishing this category of armoured vehicles.
Historically, the custom-built fully armoured assault guns usually mounted the gun or howitzer in a fully enclosed casemate on a tank chassis. The use of a casemate instead of a turret limited these weapons' field of fire, but allowed a larger gun to be fitted relative to the chassis, more armour to be fitted for the same weight, and provided a cheaper construction. In most cases, these turretless vehicles also presented a lower profile as a target for the enemy.
Sturmgeschütz (or
StuG) meaning
"assault gun" was a series of armored vehicles used by both the German
Wehrmacht and the
Waffen-SS armored formations during the Second World War that primarily consisted of the StuG III and StuG IV. The more common of the two, the StuG III, was built on the chassis of the proven Panzer III. The StuG III was initially designated "StuG" but with the creation of the StuG IV it was re-designated the "StuG III" to distinguish the two. Initially they were intended as mobile, armored gun platforms, providing close fire support to the infantry to destroy bunkers, pillboxes and other entrenched positions. As the war progressed a number of aspects of the StuG series made them a valued supplement to the Panzer forces.
A
tank destroyer or
tank hunter is a type of armoured fighting vehicle, armed with a direct-fire artillery gun or missile launcher, with limited operational capacities and designed specifically to engage enemy tanks.
Tanks are armoured fighting vehicles designed for front-line combat, combining operational mobility and tactical offensive and defensive capabilities; tanks perform all primary tasks of the armoured troops. The tank destroyer on the other hand is specifically designed to take on enemy armour. Many are based on a tracked tank chassis, while others are wheeled.
Personally, I would classify CV90-120 more as TD or heavy Recon vehicle than as StuG/Assault gun, due to relatively light armor.
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2)
could you please Identifie these 2 vehicles
@Penguin 
Thyssen-Henschel
R-400 (TH-400)
Some years ago, the then Thyssen Henschel developed a complete family of wheeled armoured fighting vehicles as a private venture called the TH-200 (4 × 4), TH-600 (6 × 6) and the TH-800 (8 × 8). Details of these were given in Jane's Armour and Artillery 1997-98. Development work on the TH-200 and TH-800 stopped some years ago and Thyssen Henschel subsequently became Henschel Wehrtechnik and development work on the TH-400 continued.With the acquisition of Thyssen Henschel by Rheinmetall DeTec, the vehicle became the H-400 and, in early 2000, the former company became known as Rheinmetall Landsysteme GmbH. More recently the designation of the vehicle has been changed yet again to the R-400. As of mid-2004 there were no plans for the R-400 to enter quantity production. The vehicle has however been used as a testbed for other Rheinmetall company subsystems.
http://www.army-guide.com/eng/product4246.html
http://www.army-guide.com/eng/product940.html
https://en.wikipedia.org/wiki/TH200
In your original post, the turret is the same as on the Argentinian TAM tank (aka TH-301, also designed by TH).
Below and example fitted with the turret of a Leopard 1 tank.
