The 17-pdr was arguably the best British anti-tank gun developed during World War II. With its standard APCBC ammunition it was capable of penetrating most German tanks. The APDS rounds introduced in late 1944 offered improved penetration and presaged the anti-tank ammunition used by post-war tanks. Some contend that the US 90mm M3 gun mounted in the M36 tank destroyer was a better anti-tank gun than the 17-pdr, but the M3 was not available for the key battles in Normandy following D-Day.

According to one British source (WO 219/2806, Appx G; see below), the 17-pdr gun mounted on the M10 was able to penetrate around 127mm of armour at 600yd (548m) and 120mm at 1,000yd (914m) using standard APCBC ammunition impacting at a 30-degree angle. When supplied, APDS ammunition could penetrate some 183mm of armour at 550m and 172mm at 1,000m at a 30-degree angle. The accuracy of the APDS round was poor during World War II, however. By comparison, the standard M10’s 3in M7 gun using APCBC ammunition could penetrate 97mm of armour at 550m at a 30-degree angle and 92mm of armour at 900m at a 30-degree angle. Only with HVAP ammunition did the M7 gun compare with the 17-pdr. US 3in HVAP ammunition was in very short supply, however, whereas the standard 17-pdr ammunition was available in quantity for the British Army.

The 17-pdr SP M10 was provided with an M51 direct-sighting telescope for direct fire, providing 3× magnification with a 13-degree field of view. Its US panoramic sight was replaced with a British dial sight and clinometer for indirect-fire artillery missions. Some units developed techniques for semi-indirect turret-down anti-tank shoots, claiming at least one kill using this approach. While the 17-pdr M10 was regularly used for indirect-fire missions, the Wehrmacht actively discouraged use of the Jagdpanther in this role for fear of excessive barrel wear and to retain the element of surprise. The No. 1 of the 17-pdr M10 was equipped with a pair of binoculars, typically Mk 2 (Kelvin Prismatic) offering 6× magnification and an 8-degree field of view or Mk V (Ross Prismatic) with 7× magnification and a 7¾-degree field of view.

The 17-pdr M10 also mounted a .50-calibre M2 heavy machine gun for antiaircraft defence on a pintle mount at the turret rear. This location was prompted by the desire to balance the weight of the turret, but it was not ideally placed for the M2’s use against ground targets, because it could only be fired from inside the turret with the turret traversed to the rear. Otherwise, a crewman had to exit the turret and fire the M2 while standing exposed on the rear engine deck. Because the M10 was already out of production by the summer of 1944, there were no factory fixes to remedy the issue. Instead, some units in the field moved the M2 from the turret rear to a front location by welding a pintle mount onto one of the forward corners, despite the adverse effect this repositioning had on the balance of the turret.

PROTECTION

The M10 was essentially an M4 medium tank fitted with thinner armour and a lightly armoured turret. Its frontal armour was only 60–75 per cent as thick as that of the M4, while the M10’s side armour was more sloped. The M10’s open turret rendered it vulnerable to mortars and artillery as well as overhead small-arms fire and grenades. It meant the No. 1 was forced to operate ‘head up’ and therefore with better vision and situational awareness than if operating closed down. Some anti-tank regiments created improvised roof armour for their vehicles. Some were of the opinion that the attitude of the No. 1 made the difference – a No. 1 who would operate with his head up would do so even if overhead cover was available; but the provision of overhead cover would not make any difference to those more cautious No. 1s who were reluctant to expose their heads.

MOBILITY

The M10c weighed 66,000lb with the 375bhp engine giving a power-to-weight ratio of around 11.5hp/ton. The M10, like the M4 on which it was based, had narrow tracks that were ill-suited to wet ground experienced in North-West Europe. Extended end-connecters offered better floating qualities on mud, but could catch on the hull overhang.

The General Motors 6/71 Diesel Model 6046 ‘twin six’ engine was formed from two Detroit Diesel 6-71 inline engines mated to a single output. The tandem engine produced 375bhp (280kW) at 2,100rpm. One of the engines could be disconnected at will from the output and run independently so if one was knocked out or broke down, the other engine could be used to move the vehicle, albeit much more slowly. The M10A variant of the M10 was powered by the Ford GAA V-8 petrol engine, an eight-cylinder derivative of a V-12 aircraft engine project. It nominally delivered 500bhp (373kW) at 2,600rpm, but its actual performance was about 450bhp (336kW) at 2,600rpm, giving it comparable performance to the diesel version. The M10A was retained in the United States for training.

A tracked vehicle’s basic mechanism of steering can be quite brutal, as it relies on one track slewing or skidding over the ground. Both the M10 and the Jagdpanther used a form of differential gearing that engaged a lower gear on one side than the other and produced a lower speed on one side than the other, which was less extreme than more primitive brake-and-clutch systems. The M10 shared its combined transmission, differential and final drives, called the ‘Powertrain’, with the M4 tank. The M10 had a turn radius of 26ft in first gear and 50ft in fifth. The Powertrain was robust and could tolerate abuse by heavy-handed driving in a manner that might break the more delicate Jagdpanther mechanism. For maintenance purposes, the M10’s final drive could be accessed by unbolting the cover on the glacis plate.

The M10 had the vertical volute spring suspension (VVSS) of the M3 and M4 medium tanks. This was a robust system; it was easily maintained and units could be much more readily replaced and with much less labour than those of the Jagdpanther.

The armoured hull of the M10 was not watertight because it was not envisaged that the M10 would need to cross rivers in tactical settings, but it could and would be prepared for deep wading for amphibious operations such as the Normandy landings. Preparing the vehicle for wading watertight

1. 17-pdr APDS Shot
2. 17-pdr APCBC Shot
3. Gunner’s traverse handwheel
4. Gunner’s M51
telescopic sight
5. Gun travel lock
6. QF 17-pdr Mk II in M5 mount
7. Folding brace for turret
roof tarp
8. Sten machine carbine
9. Commander’s seat
10. Loader’s seat
11. Gunner’s seat
12. .50in Browning machine gun

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