In computer science's object-oriented programming, class variables (static fields) contain information which is associated with all instances of a class. If all tanks have one cannon, then it is not necessary to specify, in an instance variable for each tank object, that each tank has only one cannon; rather, one can simply define a class variable which does this and thus all instances of the class will share the variable.
... and Spain.
In 1985 France withdrew in favour of the 100% French Avions de Combat Expérimentaux (ACX) project (which later became the Dassault Rafale).
The remaining ...