longer barrel and used a larger propellant charge giving far superior armor penetrating capabilities. The 17pdr SP was used by the British, Canadian and Polish armies in Italy and northwest Europe. As well as service with British forces in Northwest Europe, they were retained post-war. Those not upgunned were stripped of their turrets and used as artillery tractors. In British service, as self-propelled anti-tank guns, the M10 was operated by regiments of the Royal Artillery. Typically, two batteries had M10s while the other two batteries had the towed 17-pounder gun. One tactical theory was that the two towed batteries would form a gun line, while an M10 battery remained mobile on each flank to drive or lead enemy tanks to the static gun line. In practice, UK batteries were frequently separated in Normandy, M10s being seconded to British tank brigades equipped with Churchill tanks armed with the general purpose 75 mm gun just as were British 17 pounder conversions. Free French Army The Free French received at least 227 M10s, 155 of them through Lend-Lease. They served first in Italy, then in France and Germany. During the liberation of Paris in August 1944, a single M10 of General Leclerc's 2nd Armored Division named "Siroco" disabled a Panther in the Place de la Concorde from under the Arc de Triomphe on the Place de L'Etoile, at 1800 m. French M10s also saw action on the French-German border around Strasbourg and in southern Germany; the Free French First Army led by General De Lattre received some when they were a part of the Sixth United States Army Group. French M10s were operated along similar lines as US tank destroyer units, although initially with five vehicles per platoon instead of four. Red Army Approximately 52 M10s were supplied to the Soviet Union through Lend-Lease. They were used to form two self-propelled artillery regiments (SPA). The first was the 1223rd Self-propelled Artillery Regiment of the 29th Tank Corps, part of the 5th Guards Tank Army. This unit served on the 3rd Belorussian Front in 1944, taking part in summer campaigns in Belorussia, the Baltic, and East Prussia. The 1239th Self-propelled Artillery Regiment was part of the 16th Tank Corps, 2nd Tank Army. It fought in Belorussia and Poland in 1944. Germany In 1944, during the Battle of the Bulge, Operation Greif was a plan developed by the Nazis to infiltrate behind the allies lines.