Blow-up Weapons

Not exploding ones, weapons that are filled with air. There's an interesting article at BBC News about Russian inflatable weapons.

A turret appears, then out pops a long plastic gun barrel. This is an inflatable Russian tank. ... When the men pump up their next piece of plastic, this one expands into a S-300 rocket launcher, complete with giant truck and inflatable rockets. ... waiting to be blown up are inflatable MiG fighter jets - even entire Russian radar stations. ... They are made of a special material that tricks enemy radar and thermal imaging into thinking they are real weapons.

One thing that the Soviet military was very good at in World War Two was deception. They call it maskirovka, and it has been a fundamental feature of Soviet and now Russian military doctrine. As Globalsecurity.org points out,

The goal of maskirovka is to make the enemy concentrate his forces against false threats and uselessly expend his means of destruction on them. ... they also do it actively, through the use of dummy structures, electronic warfare, false maneuvers, and various other methods.

These blow-up dummies are cheap and have the potential to be extremely effective, not just in manipulating enemy intelligence/observations, but in causing significant diversions of resources away from real threats. These dummies might actually cause more problems for an opponent than some real weapon systems.