Tank Destroyer

Tanks with powerful guns but lacking a rotating turret. Weak to infantry and quick moving vehicles, but their gun packs quite a punch.

Strategy
Tank destroyers are best used as ambush vehicles, due to the complete lack of a rotating turret. They're prone to being flanked by infantry and perform poorly in urban areas, therefore it's best to avoid them.

Background
Tank destroyers or 'Self-Propelled Guns' (SPGs) were vehicles designed to directly combat other Tanks, with a smaller focus on infantry support. Usually SPGs would not have a rotating turret, which meant they were cheaper and easier to produce. One Panzer IV G cost Germany ~103,500 Reichsmark, while a Stug III only cost 82,000 Reichsmark. The numbers produced back this up as there were only close to 5,800 Panzer IIIs produced versus 10,000 Stug IIIs.

Usually SPGs had to sacrifice in one department of armored warfare to boost another. Sometimes, that meant the lack of a rotating turret, less armor, or a roof. Take for example the American M10 Gun Motor Carriage (GMC), a tank destroyer with a rotating turret, which also did not have a roof. Its armor however was thin which meant if the vehicle was shot at, most rounds would result in penetrations.

The Stug III and Jagdpanzer are in a similar position. The lack of a turret makes the vehicles extremely low in profile, helping conceal them in low bushes and forests. In the Jagdpanzer's case, it also allows the frontal armor to be sloped, increasing the effectiveness of it, without increasing weight and vehicle cost.