Editing Tank destroyer (section)

=== United States ===
{{Main|Tank destroyer battalion (United States)|List of tank destroyer units of the United States Army}}
{{Redirect|Gun motor carriage||Self-propelled artillery}}

[[United States Army|U.S. Army]] and counterpart British designs were very different in conception. U.S. doctrine was based, in light of the [[fall of France]], on the perceived need to defeat German [[blitzkrieg]] tactics, and U.S. units expected to face large numbers of German tanks, attacking on relatively narrow fronts. These were expected to break through a thin screen of anti-tank guns, hence the decision that the main anti-tank units—the [[Tank destroyer battalion (United States)|Tank Destroyer (TD) battalions]]—should be concentrated and very mobile. In practice, such German attacks rarely happened. Throughout the war, only one battalion ever fought in an engagement like that originally envisaged (the [[601st Tank Destroyer Battalion|601st]], at the [[Battle of El Guettar]]). The Tank Destroyer Command eventually numbered over 100,000 men and 80 battalions each equipped with 36 self-propelled tank destroyers or towed guns.

[[File:75 mm M3 GMC (cropped).jpg|thumb|The first US tank destroyer was a 75 mm gun on a half-track chassis]]
[[File:Aberdean proving grounds 036.JPG|right|thumb|[[M10 tank destroyer]]]]

Only [[Shoot-and-scoot|a few shots were expected to be fired from any firing position]]. Strong reconnaissance elements were provided so that TDs could use pre-arranged firing positions to best advantage. [[Flanking fire]] by TDs was emphasized, both to penetrate thinner enemy side armour, and to reduce the likelihood of accurate enemy return fire.

All American tank destroyers were officially known by exactly the same collective term used for American self-propelled artillery ordnance, "gun motor carriage". The designs were intended to be very mobile and heavily armed. Most of the tank-hull based designs used special open-topped turrets of a differing design from the original tank it was based on, which was meant to both save weight and to accommodate a larger gun. The earliest expedient design was mounting a [[75 mm M1897 field gun]] in a limited-traverse mount on an [[M3 half-track]], which was designated  [[M3 GMC|75 mm gun motor carriage M3]]. Another, considerably less successful, early design was the [[M6 gun motor carriage]] which mounted the US 37 mm anti-tank gun facing to the rear on the bed of a Dodge 3/4-ton light truck. 

The M3 was first used against the Japanese in the Philippines and then in the Tunisian campaign of the war in North Africa. Some were supplied to British units who used them within [[Armoured car regiment|armoured car reconnaissance regiments]] for fire support.  The M6 GMC was unarmoured and the 37 mm gun was ineffective against most enemy tanks by the time it entered service.

By far the most common US design, and the first that was fully tracked and turreted (which became the American hallmark of World War II "tank destroyer" design) was the [[M10 tank destroyer|3-inch gun motor carriage M10]], later supplemented by the [[M36 tank destroyer|90 mm gun motor carriage M36]]—both based on the [[M4 Sherman]] hull and powertrain—and the [[M18 Hellcat|76 mm gun motor carriage M18 (Hellcat)]], based on a unique hull and powertrain design, with a slight visual resemblance to what was used for the later [[M24 Chaffee]] light tank. The M18 came closest to the US ideal; the vehicle was very fast, small, and mounted a {{nowrap|76 mm}} gun in a roofless open turret. The M36 Jackson GMC possessed the only American-origin operational gun that could rival the German [[8.8 cm Pak 43]] anti-tank gun and its tank mounted variant, the [[90 mm gun M1/M2/M3|90 mm M3 gun]], and the M36 remained in service well after World War II. The only dedicated American casemate hull design fighting vehicle of any type built during the war, that resembled the German and Soviet tank destroyers in hull and general gun mounting design, was the experimental [[T28 super-heavy tank]], which mounted a 105 mm T5E1 long-barrel cannon. This gun had a maximum firing range of 12 miles (20 km), and the vehicle was originally designed as a very heavily armoured self-propelled assault gun to breach Germany's [[Siegfried Line]] defenses.

Of these tank destroyers, only the {{nowrap|90 mm}} gun of the M36 proved effective against the frontal armour of Germans' larger armored vehicles at long range.<ref>Forty and Livesey 2006 p. 117</ref> The open top and light armour made these tank destroyers vulnerable to anything greater than small-arms fire. As the number of German tanks encountered by American forces steadily decreased throughout the war, most battalions were split up and assigned to infantry units as supporting arms, fighting as [[assault gun]]s or being used essentially as tanks. In this sense they were an alternative to the [[Independent tank battalion]]s that were attached to various Infantry Divisions.

The expectation that German tanks would be engaged in mass formation was a failed assumption. In reality, German attacks effectively used [[combined arms]] on the ground, fighting cohesively. American tank destroyer battalions comprised three tank destroyer companies supported by nine security sections. The single-purpose tactics of the tank destroyer battalion failed to account for non-tank threats.<ref name="single purpose">{{cite book|last1=Gabel|first1=Christopher R.|title=Seek, Strike and Destroy: US Army Tank Destroyer Doctrine in World War II|publisher=DIANE Publishing|isbn=9781428915770|pages=68–69|url=https://books.google.com/books?id=IA1ljqnb7IwC&q=main+battle+tank+doctrine&pg=PA70|access-date=4 May 2015|year=1985}}</ref>

In the 1950s the goal of providing airborne forces with a parachute-capable self-propelled anti-tank weapon led to the deployment of the [[M56 Scorpion]] and [[M50 Ontos]]. The concept later led to the [[M551 Sheridan]] light tank of the mid-1960s.