17pdr SP Achilles

17pdr SP M10 "Achilles"
"Achilles" Self-Propelled Gun M10 at La Roche-en-Ardenne, Belgium
Type	Self-propelled anti-tank gun
Place of origin	United Kingdom
Production history
Manufacturer	converted by Royal Arsenal, Woolwich
No. built	1,100
Specifications
Weight	29.6 tonnes (65,000 lb)
Length	7.01 m (23 ft  8 1⁄4 in) including gun 5.97 m (19 ft 7 in) excluding gun
Width	3.05 m (10 ft)
Height	2.57 m (8 ft 2 in)
Crew	5 (commander, loader, gunner, loader's assistant, driver)
Armour	9 to 57.2 mm (0.3 to 2.3 in)
Main armament	Ordnance QF 17 pounder (76.2 mm) 50 rounds
Secondary armament	.50 cal (12.7 mm) Browning M2HB AA machine gun 420 rounds .303 (7.62 mm) Bren light machine gun
Engine	General Motors 6046 diesel (twin 6-71) 375 hp (276 kW)
Power/weight	12.5 hp/tonne
Suspension	Vertical Volute Spring Suspension (VVSS)
Operational range	300 km (186 mi)
Speed	51 km/h (32 mph)

The 17 pounder, Self-Propelled, Achilles was a British variant of the American M10 tank destroyer armed with the powerful British Ordnance QF 17 pounder anti-tank gun in place of the standard 3" (76.2 mm) Gun M7. With a total of 1,100 M10s converted, the 17 pdr SP Achilles was the second most numerous armoured fighting vehicle to see service armed with the 17 pounder gun, behind the Sherman Firefly.

The name "Achilles" was officially a designation applied to both the 3" gun and 17 pounder versions (as Achilles I/II and Achilles Ic/IIc respectively) but was little used during the Second World War; at the time, the vehicle was called 17pdr M10, or 17pdr SP M10, or even occasionally, "Firefly". It has since become identified almost exclusively with the 17 pounder version.

In the wake of Germany's successful 1939–41 campaigns, US armour doctrine had incorporated the idea of fast, lightly armoured vehicles carrying high velocity anti-tank guns as the best way to deal with the fast moving armour spearheads of the German Blitzkrieg. The M10 was based on the chassis of the M4 Sherman but carried thinner although more sloped armour in order to comply with the high speed requirement for the tank. At the same time, the British had been examining the possibility of designing a low-silhouette self-propelled tank destroyer, preferably with a 360-degree traversing turret, with armour that would be able to resist the German 50 mm at 800 yards and mounting the 17 pounder. However, with the arrival of the M10 on the battlefield in late 1942, British plans for a turreted self-propelled gun were cancelled.

The M10 was first made available to the British in 1943. These vehicles were open-topped and mounted a 3-inch American gun, which was significantly more powerful than the Ordnance QF 6 pounder that was mounted on British tanks of the period and was of equal power to the 7.5 cm KwK 40 used by the Panzer IV and Sturmgeschütz III. When introduced into service in late 1942, the thin but sloped armour of the M10 provided good protection against the standard 50 mm gun mounted on most German tanks and anti-tank guns, and the 3-inch (76 mm) gun was able to easily defeat all German armour except for the handful of Tigers deployed against the Western Allies.