Tank Destroyers are important specialized units. They provide more damaging anti-tank firepower than standard tanks, without an extremely high price tag. Economy-savvy players often rely on supporting their forces with tank destroyers rather than invest in larger, more expensive combat tanks.
Despite the added anti-tank strength a tank destroyer can add to your force, it also comes with a glaring weakness -- its susceptibility to infantry and inability to target structures. Lacking high-explosive ammunition and defensive machineguns, tank destroyers can be easily destroyed by advancing infantry.
There are two primary types of tank destroyers in Spring: 1944 -- turreted, as used by the US and Britain, and turretless, as used by Germany and the Soviet Union.
Turreted Tank Destroyers
Turreted Tank Destroyers, such as the M10 Wolverine and its British cousin the Achilles are turreted -- their anti-tank guns are mounted in rotating turrets with 360-degree coverage. This allows tank destroyers a level of tactical maneuverability, as they can engage targets in any direction.
However, both of these vehicles are relatively lightly-armoured -- US tank destroyer doctrine generally favoured lightly-armoured, fast-moving vehicles that could outmaneuver heavy German tanks and attack from the flanks or rear (and the Achilles is based on an American tank destroyer design and so shares this feature). This leaves these tank destroyers vulnerable to nearly everything, from enemy infantry to light vehicles and especially tanks.
Turretless Tank Destroyers
In both cases, the idea was to provide a more offensively-powerful vehicle with equal or greater protection than other vehicles of its size. To do this, all of these designs removed the need for turrets by having the main gun placed directly on the hull. This allowed the designers to increase armour thickness and armament size while keeping the vehicles relatively light-weight, as well as greatly reduced their manufacturing costs.
The primary disadvantage, of course, was the lack of turret. This greatly reduced their tactical maneuverability, as using their main gun required turning the entire vehicle to face their targets. This makes offensive moves quite difficult and makes flank attacks next to impossible. Like turreted tank destroyers, they also lack high explosive ammunition or machineguns to protect themselves against infantry.