M4 Sherman - Armor

Armor

The steel frontal turret armor of the M4 ranged from 64–76 mm (2.52–2.99 in). The M4’s gun mantlet was also protected by 76 mm (2.99 in) of armor sloped at 30 degrees, The turret side armor was 50 mm (1.97 in) a 5-degree angle while the rear was 64 mm at a 90-degree angle and the turret roof was 25 mm thick. The hull front sported 51 mm armor. Although the Russian T-34 is often credited for introducing sloped armor in a production tank, the Sherman's upper hull was angled at 56 degrees, while the lower half of the hull was curved. The earlier U.S. M2 and M3 medium tanks also had sloped armor. The hull sides were 38–45 mm (1.50–1.77 in) thick, and vertical. The hull rear—which protected and was offset from the rear radiator on some versions—was 38 mm (1.50 in) to the vertical or sloped to 85 degrees. The hull roof was 25 mm (0.98 in).

The armor of the M4 was effective against most early war anti-tank weapons, but was easily penetrated by later German tank guns and anti-tank guns. Early versions had unfortunate shot traps, locations where the effect of slope was greatly reduced, located just in front of the driver and assistant driver. The 75 mm L/48 tank guns would penetrate up to a range of 1,370 – 1,500 meters, and larger guns could penetrate past 2,000 metres. Regardless of this vulnerability, historian John Buckley has stated the M4 was "moderately superior" to the relatively small, but older Panzer IV. Although the later modeled medium and heavy tanks were greatly feared, Buckley opined "The vast majority of German tanks encountered in Normandy were either inferior, or at least, merely equal to the Sherman."

Progressively thicker armor was added to hull front and turret mantlet in various improved models. Many had an additional rectangular patch on each side protecting ammunition stowage, others had an additional slanted plate in front of each front crew hatch. Field improvisations included placing sandbags, spare track links, concrete, wire mesh, or even wood for increased protection against shaped-charge rounds. While mounting sandbags around a tank had little effect against high-velocity anti-tank gunfire it was thought to provide standoff protection against HEAT weapons, primarily the German Panzerfaust anti-tank grenade launcher and Panzerschreck anti-tank rocket launcher. By 1945, it was rare to see a Sherman without any field improvisations. In the only study known to have been done to test the use of sandbags, on March 9, 1945, officers of the 1st Armored Group tested standard Panzerfaust 60s against sandbagged M4s; shots against the side blew away the sandbags and still penetrated the side armor, whereas shots fired at an angle against the front plate blew away some of the sandbags but failed to penetrate the armor. Earlier, in the summer of 1944, General Patton, informed by his ordnance officers that sandbags were useless and that the machines' chassis suffered from the extra weight, had forbidden the use of sandbags. Following the clamor for better armor and firepower after the losses of the Battle of the Bulge, Patton ordered extra armor plates salvaged from knocked-out American and German tanks welded to the front hulls of tanks of his command. Approximately 36 of these up-armored M4s were supplied to each of the armored divisions of the Third Army in the spring of 1945.

The M4A3E2 Sherman Jumbo variant had even thicker frontal armor than the Tiger I, with a totally flat sloped glacis plate, having no protrusions from the forward crew hatchways which the original M4 designs possessed and a thicker welded mantlet for the main gun. Intended for the assault to break out of the Normandy beachhead, it entered combat in August 1944.

The M4 had an escape hatch on the hull bottom to help the crew survive and, in the Pacific, Marines used this Sherman feature in reverse to recover wounded infantry under fire. Combat experience indicated the single hatch in the three-man turret to be inadequate for timely evacuation, so Ordnance added a loader's hatch beside the commander's. Later M4s also received redesigned hull hatches for better egress.

Research conducted by the British No. 2 Operational Research Section, after the Normandy campaign, concluded a Sherman would be set alight 82% of the time following an average of 1.89 penetrations of the tank’s armor; in comparison they also concluded the Panzer IV would catch fire 80% of the time following an average of 1.5 penetrations, the Panther would light 63% of the time following 3.24 penetrations, and the Tiger would catch fire 80% of the time following 3.25 penetrations. John Buckley, using a case study of the 8th and 29th Armoured Brigades found that of the 166 Shermans knocked out in combat during the Normandy campaign, only 94 were burnt out; 56.6%. Buckley also notes that an American survey carried out concluded that 65% of tanks burnt out after being penetrated. United States Army research proved that the major reason for this was the stowage of main gun ammunition in the sponsons above the tracks. A U.S. Army study in 1945 concluded that only 10–15 percent of wet-stowage Shermans burned when penetrated, compared to 60–80 percent of the older dry-stowage Shermans

At first a partial remedy to ammunition fires in the M4 was found by welding 1-inch-thick (25 mm) appliqué armor plates to the sponson sides over the ammunition stowage bins. Later models moved ammunition stowage to the hull floor, with additional water jackets surrounding the main gun ammunition stowage. The practice, known as "wet stowage", reduced the chance of fire after a hit by a factor of four. The Sherman gained grim nicknames like "Tommycooker" (by the Germans, who referred to British soldiers as "Tommies"; a tommy cooker was a World War I era trench stove). The British took to calling it the "Ronson", the cigarette lighter which had the slogan "Lights up the first time, every time!" Polish tankers referred to it as "The Burning Grave".

Many think that the fires for which the Sherman is infamous were a result of its gasoline engine. Actually, most of the tanks of the time used gasoline engines. Fuel fires occasionally occurred, but such fires were far less common and less deadly than ammunition fires. In many cases the fuel tank of the Sherman was found intact after a fire. Tankers describe "fierce, blinding jets of flame," which is inconsistent with gasoline-related fires but fits cordite flash.

The armor of the Sherman comparatively to the Panther can be described by statements used in a report to General Eisenhower at SHAEF:

I have actually seen ricochets go through an M4 at 3000 yards. I have seen HEAT fired from a 105mm Howitzer at a Mark V at 400 yards. The track was hit and damaged, and a direct hit on the turret only chipped the paint.