page_title: 17pdr SP Achilles
section_title: Design
hierarchical_section_title: 17pdr SP Achilles / Design
caption_attribution_description: IWM caption&#160;: THE BRITISH ARMY IN ITALY 1944. An Achilles 17pdr tank destroyer crossing the River Savio on a Churchill ARK which was driven into the river
context_page_description: The 17pdr SP Achilles was a British variant of the American M10 tank destroyer armed with the British Ordnance QF 17 pounder high-velocity 76.2 mm anti-tank gun in place of the M10's considerably less powerful 3 inch Gun M7. A total of 1,100 M10s were converted to Achilles, making it the second most numerous armoured fighting vehicle to carry 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 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.
context_section_description: The 17 pdr SP Achilles was basically a modified M10, the principal difference being the gun. The main armament of the Achilles was the Ordnance QF 17 pounder, a substantially more powerful gun than the 3 in (76.2 mm) M7 mounted on the standard M10. The single top-mounted .50 calibre M2 Browning heavy machine gun was retained.
  The 17 pounder mounted on the Achilles was able to penetrate some 140 mm of armour at 500 m (550 yd) and 131 mm at 1,000 m (1,100 yd) using standard Armour Piercing, Capped, Ballistic Capped (APCBC) ammunition impacting at a 30-degree angle. When supplied, Armour-piercing discarding sabot (APDS) ammunition could penetrate some 209 mm (8 inches) of armour at 500 metres and 192 mm at 1,000 metres at a 30-degree angle, though the accuracy of the APDS round was poor during the war.  In comparison, the M7 gun on the standard M10 using the same type of ammunition (APCBC) would penetrate 98 mm of armour at 500 m at a 30-degree angle, and 88 mm of armour at 1,000 metres at a 30-degree angle. Only with High Velocity Armour Piercing (HVAP) ammunition did that gun compare with the 17 pounder, the ammunition being able to penetrate 140 mm at 500 m at a 30-degree angle, and 127 mm at 1,000 m at a 30-degree angle. However, HVAP ammunition was in very short supply, whereas the standard 17 pounder ammunition was available in huge quantities for the British.
  The 17 pounder required a counterweight fitted behind the muzzle brake on its long barrel. This gave the Achilles a distinctive appearance compared to the comparatively short-barrelled, brakeless, entirely straight barrel of the M10.  Once the Germans discovered the effectiveness of the Achilles' gun on the same M10 carriage as the much less powerful M7 gun, attempts were made to disguise the 17 pounder by painting its brake and counterweight.
  Two other material changes were made to the Achilles: the addition of 17 mm (0.67 in) thick armour plates welded to the front and sides of the M10 to increase armour protection; and the M10's open turret was fitted with a 20 mm thick shield to provide protection from overhead threats.
caption: An Achilles 17pdr Self-propelled anti-tank gun crossing the River Savio on a Churchill ARK which was driven into the river, 24 October 1944
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