Editing M4 Sherman (section)

===Gun development===
As the Sherman was being designed, provisions were made so that multiple types of main armament (specified as a 75&nbsp;mm gun, a 3-inch gun, or a 105&nbsp;mm howitzer) could be mounted in the turret.{{sfn|Hunnicutt|1978|p=198}} The possibility of mounting the main gun of the [[M6 heavy tank]], the [[3-inch Gun M5|3-inch gun M7]], in the turret of the M4 Sherman was explored first, but its size and weight (the weapon was modified from a land-based antiaircraft gun) made it too large to fit in the turret of the Sherman. Development on a new 76&nbsp;mm gun better suited to the Sherman began in fall 1942.

In early 1942, tests began on the feasibility of mounting a 105&nbsp;mm howitzer into the turret of the Sherman. The basic [[M101 howitzer|105&nbsp;mm howitzer M2A1]] was found to be ill-designed for mounting in a tank turret, so it was completely redesigned and re-designated the 105&nbsp;mm howitzer M4. After modifications to the turret (concerning the balancing of the gun and the strength of the power traverse) and interior of the hull (concerning the stowage of the 105&nbsp;mm ammunition), the Ordnance Department expressed its approval of the project, and production of M4 tanks armed with 105&nbsp;mm howitzers began in February 1944.{{sfn|Hunnicutt|1978|p=208–210}}

The Sherman would enter combat in 1942 equipped with the [[75 mm Gun (US)#M3 2|75&nbsp;mm gun M3]], a 40-[[Calibre length|caliber]] gun that could penetrate an estimated {{convert|88|mm|in|abbr=on}} of [[rolled homogeneous armor]] (RHA) at 90 degrees, a range of {{convert|100|m|yd|abbr=on}} and {{convert|73|mm|in|abbr=on}} at {{convert|1000|m|yd|abbr=on}} firing the usual M61 APCBC round, and equipped with an M38A2 telescopic gunsight.<ref name="M4A3">{{cite book|last1=Bird |first1=Lorrin Rexford |last2=Livingston|first2=Robert D.|title=WWII Ballistics: Armor and Gunnery|date=2001|publisher=Overmatch Press|pages=62–63}}</ref> Facing the early [[Panzer III]] and [[Panzer IV]] in North Africa, the Sherman's gun could penetrate the frontal armor of these tanks at normal combat ranges, within {{convert|1000|yd|m|abbr=on}}. U.S. Army Intelligence discounted the arrival of the [[Tiger I]] in 1942 and the [[Panther tank]] in 1943, predicting that the Panther would be a heavy tank like the Tiger I, and doubted that many would be produced. There were also reports of British [[Ordnance QF 6 pounder|QF 6-pounder]] (57&nbsp;mm) guns being able to destroy the Tiger I. However, this only happened at very close ranges and against the thinner side armor.{{citation needed|date=March 2021}} Due to their misconceptions related to this, and also due to tests that seemed to prove that the 76&nbsp;mm gun was able to destroy both the Tiger and the Panther, the leadership of Army Ground Forces were not especially concerned by the Tiger I. The criteria and results of the 76&nbsp;mm gun tests were later ruled to have been inaccurate when compared to real-world conditions (tests against sections of American armor plate configured to resemble those found on a Panther tank suggested that the new M1A1 gun would be adequate, but testing against actually captured Panther tanks was never done), with Eisenhower even remarking that he was wrongly told by Ordnance that the 76&nbsp;mm could knock out any German tank. The Army also failed to anticipate that the Germans would attempt to make the Panther the standard tank of their panzer divisions in 1944, supported by small numbers of Tiger I and IIs.{{sfn|Zaloga|2008|p=94-97}}

{| class="wikitable"
|+Effectiveness of common American tank guns<ref>{{Cite book|author=United States Department of the Army |title=Ballistic data performance of ammunition, 1948.|date=1948|publisher=U.S. G.P.O|oclc=506059988}}</ref>
!
!105&nbsp;mm
!75&nbsp;mm
!76&nbsp;mm
|-
|Lethal shrapnel pieces in a 20&nbsp;ft radius from HE round
|1,010
|950
|560
|-
|Max penetration distance on unsloped rolled homogeneous armor
|
|88&nbsp;mm <br />(100 meters)
|}
When the newly designed 76&nbsp;mm gun, known as the T1, was first installed in the M4 in spring 1943, it was found to unbalance the turret, and the gun barrel also protruded too far forward, making it more difficult to transport and susceptible to hitting the ground when the tank traveled over undulating terrain. The barrel length was reduced by {{convert|15|inch|mm|abbr=on}} (from 57 [[Caliber (artillery)|calibers]] to 52), resulting in the M1 variant. Mounting this gun in the original M4 turret proved problematic, so the turret for the aborted T23 tank project was used instead for the definitive production version of the 76&nbsp;mm M4 Shermans,{{sfn|Zaloga|2008|pp=106–08, 115–116}} along with a modified version of the gun known as the M1A1.

Despite the Ordnance Department's development of new 76&nbsp;mm and 90&nbsp;mm anti-tank guns, the Army Ground Forces rejected their deployment as unnecessary. An attempt to upgrade the M4 Sherman by installing the 90&nbsp;mm-armed turret from the T26 tank project on an M4 hull in April 1944 (referred to as the M4/T26) was halted after realizing it could not go into production sooner than the T26 and would likely delay T26 development.{{sfn|Zaloga|2008|pp=126–130}} Even in 1943, most German armored fighting vehicles (later models of the Panzer IV tank, [[Sturmgeschütz III|StuG III]] assault gun and [[Marder III]] ''[[panzerjaeger]]'' self-propelled anti-tank gun) mounted the [[7.5 cm KwK 40]]. As a result, even weakly armored light German tank destroyers such as the Marder III, which was meant to be a stop-gap measure to fight Soviet tanks in 1942, could destroy Shermans from a distance.{{citation needed|date=March 2021}} The disparity in firepower between the German armored fighting vehicles that began to be fielded in 1943 and the 75&nbsp;mm-armed M4 was the impetus to begin production of 76&nbsp;mm-armed M4s in January 1944.{{sfn|Zaloga|2008|pp=115–16}} In testing before the [[invasion of Normandy]], the 76&nbsp;mm gun was found to have an undesirably large muzzle blast that kicked up dust from the ground and obscured vision for further firing. The M1A1C gun, which entered production lines in March 1944, was threaded for a muzzle brake, but as the brakes were still in development, the threads were protected with a cap. The addition of a [[muzzle brake]] on the new M1A2 gun (which also incorporated a faster rifling twist leading to a slight accuracy increase at longer ranges) beginning in October 1944 finally solved this problem by directing the blast sideways.{{sfn|Zaloga|2003|pp=10–11}}

Army doctrine at the time emphasized the multirole ability of the tank, and the capability of the high explosive shell was considered important. Being a dedicated anti-tank gun, the 76&nbsp;mm had a much weaker high explosive shell than the existing 75&nbsp;mm and was not initially accepted by various U.S. armored division commanders, even though many had already been produced and were available. All of the U.S. Army M4s deployed initially in Normandy in June 1944 had the 75&nbsp;mm gun.{{sfn|Zaloga|2008|pp=129–131}} Fighting against Panther tanks in Normandy quickly demonstrated the need for better anti-tank firepower, and the 76&nbsp;mm M4s were deployed to [[First United States Army|First Army]] units in July 1944. [[Operation Cobra]] was the combat debut of the 76&nbsp;mm gun-armed Sherman, in the form of the M4A1(76)W.{{sfn|Zaloga|2008|p=93}} General [[George S. Patton]]'s [[Third United States Army|Third Army]] were initially issued 75&nbsp;mm M4s and accepted 76&nbsp;mm-armed M4s only after the [[Battle of Arracourt]] against Panther tanks in late September 1944.{{sfn|Zaloga|2008|pp=166, 193}}

[[File:Sherman m4a2e8 cfb borden 3.JPG|thumb|M4A2(76) HVSS with T23 turret and later 76&nbsp;mm gun's muzzle brake; it also sports fenders, usually omitted on U.S. vehicles to ease maintenance]]
The higher-velocity 76&nbsp;mm gun gave Shermans anti-tank firepower equal to many of the German vehicles they encountered, particularly the Panzer IV and StuG III, but its gun was inferior to that of the Tiger or the Panther. The 76&nbsp;mm could penetrate {{convert|125|mm|in|abbr=on}} of unsloped RHA at {{convert|100|meters|yards|abbr=on}} and {{convert|106|mm|in|abbr=on}} at {{convert|1000|meters|yards|abbr=on}} using the usual M62 round.<ref name="Overmatch Press">{{Cite book|title=World War II Ballistics: Armor and Gunnery|last1=Bird|first1=Lorrin|last2=Lingston|first2=Robert|publisher=Overmatch Press|year=2001|location=Albany, NY USA|pages=60, 62|oclc=71143143}}</ref>{{page needed|date=June 2022}} The M1 helped to equalize the Sherman and the Panzer IV in terms of firepower; the 48-caliber [[7.5 cm KwK 40]] (75&nbsp;mm L/48) of the Panzer IV could penetrate {{convert|135|mm|in|abbr=on}} of unsloped RHA at {{convert|100|meters|yards|abbr=on}} and {{convert|109|mm|in|abbr=on}} at {{convert|1000|meters|yards|abbr=on}}. The 76&nbsp;mm gun was still inferior to the much more powerful 70-caliber [[7.5 cm KwK 42]] (75&nbsp;mm L/70) of the Panther, which could penetrate {{convert|185|mm|in|abbr=on}} of unsloped RHA at {{convert|100|meters|yards}} and {{convert|149|mm|in|abbr=on}} at {{convert|1000|meters|yards|abbr=on}} using the usual PzGr.39/42 round.<ref name="Overmatch Press"/> The 76&nbsp;mm was capable of knocking out a Panther at normal combat ranges from the flanks or rear but could not overcome the glacis plate. Due to its 55-degree slope, the Panther's {{convert|80|mm|in|abbr=on}} glacis had a line-of-sight thickness of {{convert|140|mm|in|abbr=on}} with actual effectiveness being even greater.<!--I'm quoting the los figure here, or what the round would have to actually go through.--> An M4 might only knock out a Panther frontally from point-blank range by aiming for its turret front and transverse-cylindrical shaped mantlet, the lower edge of which on most Panthers [[Panther tank#Turret|(especially the earlier Ausf. D and A versions)]] constituted a vulnerable [[shot trap]].{{sfn|Zaloga|2008|pp=124–125}} A 76&nbsp;mm-armed Sherman could penetrate the upper frontal hull superstructure of a Tiger I tank from normal combat ranges. Although the new gun lessened the gap between the two tanks, the Tiger I was still capable of knocking an M4 out frontally from over {{convert|2000|meters|yards|abbr=on}}.<ref name=ShermanChart>{{cite web|title=Tigerfibel supplements |url=http://paijmans.net/Tanks/Tigerfibel/ShermanChart.jpg|access-date=20 May 2020}}</ref>

In late summer 1944, after breaking out of the [[bocage]] and moving into open country, U.S. tank units that engaged German defensive positions at longer ranges sometimes took 50% casualties before spotting where the fire was coming from.<ref>''Tank Tactics: From Normandy to Lorraine'' by Roman Jarymowycz, Ch. 13 "'Who killed Tiger?' The Great Scandal"</ref> The average combat range noted by the Americans for tank-versus-tank action was {{convert|800|to|900|meters|yards|abbr=on}}. Sherman crews also had concerns about firing from longer ranges, as Sherman's high-flash powder made their shots easier to spot. This, and the U.S. Army's usual offensive tactical situation, often contributed to losses suffered by the U.S. Army in Europe.<ref>"12th Army Group, Report of Operations (Final After Action Report)" Vol. XI, Wiesbaden, Germany, 1945, pp. 66–67.</ref> Even though the various gunsights fitted to the Sherman had fewer magnification settings than those fitted to German tanks, their gunners were able to use a secondary periscope that featured a far larger field of view than their German counterparts.

T4 [[APSV|High-Velocity Armor Piercing]] (HVAP) ammunition became available in September 1944 for the 76&nbsp;mm gun. The projectile contained a [[tungsten]] penetrator surrounded by a lightweight aluminum body and ballistic windshield, which gave it a higher velocity and more penetrating power. The increased penetration of HVAP allowed the 76&nbsp;mm gun to match the Panther's [[7.5 cm KwK 42]] APCR shot.<ref>{{cite web |last1=Moran |first1=Nicholas |title=US Firefly Part 3 |url=http://worldoftanks.com/en/news/21/The_Chieftains_Hatch_Firefly3/ |website=World of Tanks - The Chieftain's Hatch |publisher=Wargaming.net |date=2 January 2014 |access-date=28 October 2014 |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304023436/http://worldoftanks.com/en/news/21/The_Chieftains_Hatch_Firefly3/ |url-status=dead }}</ref> However, its performance was heavily degraded by sloped armor such as the Panther's glacis. Because of tungsten shortages, HVAP rounds were constantly in short supply. Priority was given to U.S. tank destroyer units and over half of the 18,000 projectiles received were not compatible with the 76&nbsp;mm gun M1, being fitted into the cartridge case of the M10 tank destroyer's [[3-inch Gun M5|3-inch gun M7]].{{sfn|Zaloga|2004|pp=23–24}} Most Shermans carried only a few rounds at any one time, and some units never received any.{{sfn|Zaloga|2008|pp=194–195}}

[[File:British Sherman Firefly Namur.jpg|thumb|British Firefly in [[Namur (province)|Namur]], 1944. This is an M4 composite, showing the late cast hull front with large crew hatches]]
The British anticipated future developments in German armor and began development of a {{convert|3|inch|mm|1|abbr=on}} anti-tank gun even before its 57&nbsp;mm predecessor entered service. Out of expediency and also driven by delays in their new tank designs, they mounted the powerful 76.2&nbsp;mm [[Ordnance QF 17-pounder gun]] in a standard 75&nbsp;mm M4 Sherman turret. This conversion became the [[Sherman Firefly]]. The U.S. M1 gun and the 17-pounder had nearly identical bore diameters, but the British piece used a more voluminous cartridge case containing a much bigger propellant charge. This allowed it to penetrate {{convert|174|mm|in|abbr=on}} of unsloped RHA at {{convert|100|m|yd|sp=us|abbr=on}} and {{convert|150|mm|in|abbr=on}} at {{convert|1,000|m|yd|abbr=on}} using APCBC ammunition.<ref name="Overmatch Press"/> The 17-pounder still could not penetrate the steeply sloped glacis plate of the Panther but it was expected to be able to pierce its gun mantlet at over {{convert|2,500|yd|m|abbr=on}};{{sfn|Jentz|Doyle|1995|p=129}} moreover it was estimated it would defeat the [[Tiger I]]'s frontal armor from {{convert|1,900|yards|m|abbr=on}}.{{sfn|Jentz|Doyle|1993|p=20}} However, British Army test results conducted with two Fireflys against a Panther turret-sized target demonstrated relatively poor accuracy at long range; a hit probability of 25.4% at {{convert|1,500|yd|m|abbr=on}} with APCBC, and only 7.4% with APDS.{{sfn|Moran (1 April 2012) ''US Guns, German Armour, Pt 1''}} In late 1943, the British offered the 17-pounder to the U.S. Army for use in their M4 tanks. General Devers insisted on comparison tests between the 17-pounder and the U.S. 90&nbsp;mm gun. The tests were finally done on 25 March – 23 May 1944; they seemed to show the 90&nbsp;mm gun was equal to or better than the 17-pounder. By then, production of the 76&nbsp;mm-armed M4 and the 90&nbsp;mm-armed M36 were both underway and U.S. Army interest in the 17-pounder waned. Late in 1944, the British began to produce tungsten [[Armour-piercing discarding sabot|sabot]] rounds for the 17-pounder, which could readily breach the armor of even the [[Tiger II]]; these were not as accurate as standard rounds and not generally available.

After the heavy tank losses of the [[Battle of the Bulge]], in January 1945, General Eisenhower asked that no more 75&nbsp;mm M4s be sent to Europe: only 76&nbsp;mm M4s were wanted.{{sfn|Zaloga|2008|pp=268–269}} Interest in mounting the British 17-pounder in U.S. Shermans flared anew. In February 1945, the U.S. Army began sending 75&nbsp;mm M4s to England for conversion to the 17-pounder. Approximately 100 conversions were completed by the beginning of May. By then, the end of the war in Europe was clearly in sight, and the U.S. Army decided the logistical difficulties of adding a new ammunition caliber to the supply system was not warranted. None of the converted 17-pounder M4s was deployed in combat by the U.S., and it is unclear what happened to most of them, although some were given to the British as part of Lend-Lease post-war.{{sfn|Zaloga|2008|pp=276–277}}