The first practical experience with tanks came in 1916 when the British used them during the second Battle of the Somme. Tanks had been hurredly developed to overcome the inability of any infantry force to overcome a properly supported trench line. Tanks were first used in limited numbers and without infantry support, but their initial appearance caused panic as local machine gun fire didn't seem to affect them and a rare breakthrough was achieved. Lack of infantry support and breakdowns meant the initial attack never went anywhere. Tank doctrine evolved, but the defense learned as well so that at the end of the war the tank was not yet a decisive weapon.
Part of the reason was flawed doctrine, but the bigger reason was the nature of those early tanks, easily as primitive as the early biplanes who fought it out over Flanders Fields. The British Mark IV Male tank weighed 28 tons but was powered by only 105 horsepower. The thing could barely make walking speed. Inside the unmuffled engine noise was deafening, and poor ventilation meant heat and exhaust smoke often incapacitated the crew. Crewmen could barely see out of the things and could hear nothing. Early tanks broke down every ten miles. Without radios, communications between tanks was difficult and between the tanks and headquarters impossible. Experience also showed that with proper training and experience they could be defeated.
Tanks are also quite expensive and after World War I people were tired of paying for weapons. New weapons were very low on the priority list of post-war politicians, particularly after the onset of the Great Depression. Funds for experimentation on new tanks were scarce at best. In the US Army, tanks were all but forbidden. Many infantrymen hoped the big things would just go away so they could return to "real soldiering". Given that tanks didn't fit neatly into any of the big three pre-established military specialites-- infantry, artillery or cavalry-- no one really wanted to divert scarce funds from their particular specialty. For many years the debate was primarily theoretical, fought out in journals and a limited series of military exercises where the efficacy of armor and armored tactics could be tested.
At the same time, while many infantry veterans of the Great War didn't like tanks, the utter slaughter they experienced during that war meant few wanted to go "over the top" without tanks along to support the attack. The infantry wanted tanks designed to help them neutralize defensive strongpoints. An ideal infantry tank is heavily armored and fires an effective high explosive shell, but was not seen as needing much speed. Tank killing was at best a secondary requirement.
What interest the cavalry had in tanks centered around reconnaissance. Cavalry units were all but useless during World War I, with its long, continuous front. Cavalry charges against machine gun fire amounted to a dramatic suicide pact. The cavalry very much saw itself threatened between wars. It is important to remember the love affair between soldiers and the horse persisted well into the Second World War. The pre-war officer class all regarded horsemanship as an important skill, and many military units remained horse-drawn throughout the war. Few remember that while Germany's panzer units were heavily mechanized, the vast majority of German divisions depended upon horses for transport. Soldiers were reluctant to give up on the horse, but the cavalry longed for a mission. The only practical missions available were scouting and screening. Also, if those tank-things were going to be built and funded, cavalrymen wanted a piece of the pie. The ideal cavalry tank was seen as fast and lightly armored, capable of protecting itself but not slugging it out against strong defenses.
So as World War II began most armies fielded two types of tanks. Infantry tanks included the German Panzerkampfwagen IV, the French Char B and British Mathilda. Calvalry (or in British parlance cruiser) tanks included the Panzerkampfwagen III, the French Somua, the British Cruiser Mk I, along with the Czech TNH series (known as the Panzer 38(t) in German service) and the American M2 light.
The United States entered the war particularly ill-suited for armored warfare. The United States Tank Corps was disbanded in 1920, with all existing tanks assigned to the infantry, and the only tanks America possessed for most of the interwar years were either WWI leftovers or prototypes. Funding was virtually zero with a development budget of $100K for fiscal year 1939. Because tanks legally assigned to the infantry by the Defense Act of 1920, American thinking consisted of infantry support vehicles which were too light to perform what was expected of an "infantry tank" and combat cars, which were cavalry tanks renamed to meet the law. But the US gave a great deal of thought (which was free) and experimentation on the idea of defeating enemy armor. US Army doctrine was that tanks were supposed to assist the infantry in breaching prepared defenses. Period. Tank against tank combat does not seem to have been considered.
1940Then Germany invaded Poland in 1939. The world was at war, and generals were about to find out if they had guessed right about the shape of the next war. Nazi Germany came closest to getting it right. Their best theorist, Heinz Guderian, enjoyed Hitler's ear and the Fuhrer liked exotic, new technologies. The Wehrmacht used a very realistic set of exercises to test armored doctrine and wring out its weaknesses while Hitler got them the weapons they wanted. Superior tactical doctrine enabled Germany to whip France and England very quickly. What became known as blitzkrieg tactics was really the exploitation of two important tactical principles, surprise and concentration of force (or mass). The Germans concentrated their armor in narrow fronts. Most allied divisions had their own dedicated anti-armor weapons which inflicted losses. But the few spread out guns encountered could not inflict decisive losses against such numbers, so the German forces quickly passed through and continued their attack into areas where there were few, if any, effective anti-tank weapons. They would, as Patton so eloquently put it, "get back there amidst the cooks and the quartermaster corps. These people are not used to cordite!" Once past the anti-tank belt losses dropped sharply. Continuous movement helped protect the fast moving panzers, as knowing where a mechanized force was two hours ago is very different from knowing where it is now. Speed made it hard to reform a solid defense line. In 1940 the Luftwaffe enjoyed real, if not entirely uncontested, air superiority, and could hit possible counterattacks before they formed, and help secure the panzers' flanks. German commanders led from the front and the Luftwaffe was a fine-tuned for ground attack. None of this would have been possible in 1917, before radios become portable, cheap and reliable enough to be installed in individual armored vehicles. Every German tank had a radio. In World War I generals lost control of the battle almost from the moment it was initiated. In World War II, improved communications made it possible to adjust tactics on the fly. Battles became manageable. The German mix of concentrated armor, widespread use of radio communications, continuous movement and combined arms tactics put them well up on everyone.
Tactical superiority allowed the Germans to quickly conquer France, and to swallow whole Russian armies whole in the early days of that conflict. Of course there was a solution to the new German tactics. Deploy anti-tank belts in depth so the panzers can't just fight their way past a thin screen. Counterattack in strength into the attackers exposed flanks, and try to cut off the lead tanks from their logistics train. The French figured this out and tried, but too late to accomplish more then buying the Brits time to evacuate.
German victories drove early tank destroyer doctrine. The panzer divisions moved fast, so an effective defense required fast mobile forces to get in front of attacking armor before it could break into open country. In 1941 the US Army formed the Tank Destroyer Command to develop tactics and equipment capable of defeating all enemy tanks. Army Ground Forces commander General Leslie McNair had written the US Army's primary treatise anti-tank operations, and stressed fast, highly mobile battalions dedicated to fighting tanks. McNair accomplished much good such as ensuring all US combat vehicles deployed met high standards of automotive reliability and durability. But he had his blind spots. McNair was also an artilleryman and preferred traditional towed guns for fighting tanks. Towed guns had the advantage of being much cheaper to both build and maintain, and a lower profile which was potentially easier to camouflage. Once McNair even ordered the complete conversion of all TD battalions to towed guns. But the Tank Destroyer Center's first commander, Col. Andrew Bruce disagreed vehemently with McNair on the shape of future tank destroyers. Bruce argued towed guns were too slow and vulnerable to defeat a massed armor attack. Bruce's ideal tank destroyer had a really big gun on a really fast chassis so it could get ahead of the attacking Panzers. The debate between towed and tracked advocates was spirited, and led to the Army going to war with Tank Destroyer Battalions that were divided between tracked, armored tank destroyers and towed guns. The US also made a basic miscalculation in that they planned their guns to defeat existing German tanks (then the Pzkw III and IV) while failing to realize that as they upgraded their equipment so might the enemy, a point driven home in 1944 when they met Panther tanks in quantity.
Early in the war the US Army tried mounting an old French 75 gun on a halftrack, but the portee mount performed poorly at Kasserine Pass. The standard 37mm towed gun was also seen as obsolete immediately. US forces adopted the British six-pounder (the M1 57mm in US service) and quickly cobbled together their own towed gun out of a three-inch anti-aircraft gun on a howitzer chassis. The resulting M5 was a poor gun. It was tall and tall, heavy and difficult to emplace and lacked penetrating power, particularly in comparison with the most common German anti-tank gun of the war, The German 75mm PaK 40. Fortunately McNair had been overruled even before Kasserine pass, and armored tank destroyers well under development. The US produced three which saw common service. All were tracked and turreted, although the turret roof was conspicuous by its absence. The most common early in the war was the M10 Wolverine, which used the proven Sherman chassis with a modified 3" anti-aircraft gun. The Wolverine was there from beginning to end, but lacked the ability to engage German Panther and Tiger tanks at range.
Ordinance wanted to keep the 76mm (3"), but was talked into converting a 90mm anti-aircraft gun because the bigger gun "would be needed to penetrate Siegfried Line fortifications". The Siegfried Line was a ruse, for the Army had met some Tigers in North Africa and quickly learned that even the 76 on the M10 wasn't enough. The M36 Jackson was an M10 with the 90mm gun, and was the only US TD capable of engaging Panthers and Tigers at range. The final design was very different. The M18 Hellcat matched Bruce's ideal of a truly fast TD. It combined the 76mm gun, a torsion bar suspension and a big motor (the 400hp Continental radial from the much heavier Sherman) in a low, modern clean sheet design that was cramped and lightly armored but faster then any armored vehicle until the M1 Abrams.
While American military leaders observed the war and tried to draw lessons from across the Atlantic the Brits were actually fighting for their lives. While they may have agreed that tanks weren't suppposed to fight tanks he fact of the matter was they did fight, and fought often. They also recognized that if they were trying to improve their tanks the Germans would likely do the same. The British Army did invest in towed guns, and moved to heavier guns quickly. They also enjoyed one big asset, the 75mm OQF 17-pounder. The gun's high explosive ammunition was nothing to write home about, but in penetrating armor the 17-pounder was every bit the equal of the German 88mm. The Brits began adapting their Shermans for the big gun creating the Sherman Firefly. They tried to deploy one Firefly with each platoon of four Shermans. They also tried to deploy the gun elsewhere, including putting the 17-pounder into their M10 to create the M10 Achilles. They built an open casemate mount on a Valentine chassis to create the 17pdr SP Archer.
The Germans came by their tank destroyers differently. Once the winter of 1941-42 and the sheer size of Mother Russia put an end to their initial offensive, they quickly realized they had a problem. The Russian T34 was far better then anything they had, with a big gun, speed and well shaped armor. In fact, the T34 was good enough that a few still serve today. No German tank in 1941 had the firepower to fight the T34. Worse, like the Sherman, the T34 was designed for mass-production. The Russians built over 84,000 T34s before the war ended, while producing many other types and receiving M4 Shermans and M3 Grants from the US. Given that the Germans never produced that many tanks of all types during the war, the Wehrmacht became desperate for anti-tank vehicles with an effective gun. They could not just produce more of their own tanks. German production techniques and designs were poorly adpated to mass production, and war makes you hurry. So the Germans improvised. They converted captured French and Czech chassis, and converted obsolete PzKw I and PzKw II tanks into the Marder by simply building a big stationary fighting compartment and mounting a 75mm Pak 40. But even for their clean-sheet designed TDs (often called assault guns) the Germans stuck with casemate mounts which were easier to build but limited the main gun's traverse to only a few degrees. The Sturmgeshutz III used a PzKw III chassis, and was upgunned to permit it to carry a long STuk 40 75mm gun for fighting tanks. The Czech 38(t) chassis was adapted into the tiny Hetzer which saw service with Swiss forces into the 1970s. The Jagdpanzer was purpose built out of the PzKw IV chassis and the big 88mm gun. The Jagdtiger used the Panther's suspension. They even built the enormous Elefant tank destroyer with an 128mm gun.
Russian designs tended to follow German lines in that the used casemate mounts with limited traverse with relatively heavy armor and a big gun. The Russian SU-85 and SU-100s used an 85mm gun with a well shaped hull and proved very effective. The SU-100 remained in service into the 1970s in the Middle East.
American tank destroyers used light armor and turret mounted guns. German TDs all carried a fixed gun with limited traverse. That meant you had to aim the vehicle, a significant disadvantage. On the plus side (except for the ungainly Elefant and the cobbled-together Marder) they enjoyed a lower silhouette then the American designs and for the most part were much more heavily armored.
In action the American towed Tank Destroyer battalions were a failure, and were all but abandoned by the end of the war thanks to poor effectiveness and high casualties among gunners. Most were used as conventional artillery battalions. Much of the reason was the poor design of the M5 towed gun, but for most of the war the Allies were on the offensive. Towed guns take time and effort to emplace and camouflage, a task better suited for defensive operations when you often have more time to prepare. When the Germans counterattacked, the guns were easily bypassed. The mechanized tank destroyers fared much better, but they were rarely employed as doctrine directed. The M18 was only used once as Bruce envisioned, when its speed was used to block the roads to Bastogne during the early phases of the the Battle of the Bulge. In that defensive battle, TDs performed well, the only time they were used as doctrine intended. As the Allied armies spent 1943-5 on offense TDs ended up being used as tanks where their open turret and lighter armor proved a serious disadvantage (many crews welded scavenged armor on to create makeshift turret roofs). The US Army realized their doctrine had failed and they were better off upgunning tanks. With the 90mm armed M26 Pershing and improved variants of the Sherman in production there seemed little reason to keep the TDs in production and the Tank Destroyer force was disbanded after the war.
German TDs were also used as tanks, but out of desperation. They were good weapons, but the limited-traverse casemate mounts proved a serious disadvantage. But the net result was that tank destroyers as a group were largely abandoned at the end of World War II. For the expense and manpower required, most armies learned it was simply better to use another tank.
Cold War Tank DestroyersAfter the war most of the big gun tank destroyers were abandoned, although the SU-100 and Jagdpanzer 38(t) Hetzer served on into the 70s. West Germany and Britian developed big gun variants to match the mass of Soviet tanks they might face. The Tank Destroyer enjoyed a renaissance in the 1960s as guided anti-tank missiles began to become available. These weapons required a much lighter chassis then an effective high-velocity gun, allowing a jeep or an armored personnel carrier to serve as an effective chassis. In a sense many modern APCs, including all IFVs including the Bradley Fighting Vehicle and the Russian BMP serve in the role of a tank destroyer. The M1128 version of the US Army's Stryker APC and other wheeled AFVs mount big guns which can prove quite effective against the older tanks often found in the developing world.
Today, most soldiers consider the best anti-tank vehicle to be another tank. The heyday of the Tank Destroyer came during World War II when thousands of TDs served but never lived up to the job that was expecting them. Instead of killing enemy tanks, they served as tanks themselves or mobile artillery, jobs for which tanks and purpose built self-propelled guns served better.
A World War II propaganda film for the M10 you may enjoy! http://www.youtube.com/watch?v=LL6vl0RCpOk
A brief documentary on the M18 http://www.youtube.com/watch?v=BuL-WXPg_OY&feature=related
A slideshow from the 612th TD battalion http://www.kodakgallery.com/gallery/sharing/slideshowFinishPage.jsp?token=728418826805:1288216411
A good site on all German vehicles http://www.achtungpanzer.com
A restored German Sturmgeschutz (StuG IV) running http://www.youtube.com/watch?v=TZwkJbTcjZI&feature=related