I previously posted some photos from trials of the armour skirts of a captured Pz.Kpfw.III Ausf.N tank. It turned out that the skirts themselves were not very difficult to penetrate, but they destabilized small projectiles enough to prevent penetration of the main armour, as well as offer a few other benefits. Here are some more results from that same test.
"RPG at close range. Photo #3. Penetration in the spaced armour plate (the main armour does not have damage."
This of course was not the RPG-7 made famous long after the war, but the much earlier RPG-6, an anti-tank hand grenade. As you can see, the explosion happens at a safe distance from the main armour and the grenade has little effect.
Next, the RES anti-tank rifle. This rifle was a lot more powerful than the 15-II or Blum rifle. It fired a whopping 20 mm round and had a significantly larger casing (see the photo below). Even this round does not penetrate the side armour (although here Yuri Pasholok states that it can do so from 100 meters).
"Photo #4. Hit from the RES anti-tank rifle.
- Range: 400 meters. Complete penetration in the side without spaced armour.
- Range: 200 meters. Dent in the side armour after penetration of the spaced armour."
Larger guns such as the Sherman's 75 mm gun were also tried, against which the skirts turned out to be useless.
"Photo #17. Hit by an armour piercing round from the 75 mm gun. Range: 1000 meters, angle of impact 60 degrees. The spaced and main armour were penetrated."