M6
The BMW M6 is a high-performance grand tourer automobile produced by BMW's M division, serving as the top-tier variant of the 6 Series lineup across three generations from 1983 to 2018.[1][2] Initially launched as the E24-based M635CSi (badged M6 in North America) with a 3.5-liter inline-six engine producing around 260 horsepower, the model emphasized a blend of long-distance touring comfort and track-capable dynamics derived from BMW's motorsport heritage.[3] The line was revived in 2005 with the E63/E64 generation, featuring a naturally aspirated 5.0-liter V10 engine delivering up to 500 horsepower, though it drew criticism for its hefty curb weight exceeding 4,000 pounds and the divisive sequential manual gearbox (SMG).[4][5] The final F12/F13/F06 iteration from 2012 shifted to a twin-turbocharged 4.4-liter V8 with outputs reaching 600 horsepower in Competition variants, available in coupe, convertible, and four-door Gran Coupe body styles, prioritizing refined grand touring prowess over pure agility despite advanced carbon-fiber reinforced plastic components in the roof and other areas.[6][7] Key defining characteristics of the M6 include its evolution from a homologation-inspired coupe rooted in the E24 6 Series platform introduced in 1976 to a modern flagship emphasizing turbocharged power and adaptive suspension, often positioning it as a more luxurious alternative to the sharper M3 or M5 siblings.[8] Production emphasized hand-assembled engines and M-specific tuning, with notable achievements in endurance racing through derivatives like the M6 GTLM, which competed in IMSA WeatherTech SportsCar Championship events and secured class victories. However, the model faced reliability controversies, particularly with the second-generation V10's high maintenance costs and the third-generation S63 V8's propensity for excessive oil consumption due to faulty piston rings, issues documented in owner forums and service bulletins despite BMW's performance claims.[9] Discontinued after 2018 without a direct 6 Series successor, the M6's role was largely absorbed by the BMW M8, reflecting shifting market preferences toward SUVs and sedans over traditional coupes.[9]Military equipment
Tanks and armored vehicles
The M6 Heavy Tank was an American heavy tank project initiated by the US Army Ordnance Department in December 1940, prompted by intelligence reports of German heavy panzer developments and the need for a counter to fortified positions in potential European theaters.[10] Design work emphasized layered armor up to 4 inches thick on the hull front and turret, with a 3-inch M7 gun in a hand-rotated turret, supplemented by machine guns.[11] Twelve pilot models were completed by September 1941, followed by limited procurement of 28 additional units for testing, totaling 40 vehicles produced between 1942 and 1943 at Fisher Body Division plants.[12] Weighing approximately 57 short tons in combat configuration, the M6 relied on two Chrysler A57 multibank engines—each a compact assembly of four inline-six cylinder blocks configured as V8s, delivering 425 horsepower apiece for a combined output enabling a top speed of 22 mph on roads.[11] Ground clearance measured 20.5 inches, providing reasonable obstacle negotiation despite the vehicle's 27-foot-8-inch length and 10-foot-2-inch width, though its height of 9 feet 10 inches complicated camouflage and rail loading.[13] Suspension utilized vertical volute springs on a Christie-derived system, supporting the mass while maintaining a power-to-weight ratio of about 8 hp/ton, which empirical trials confirmed as adequate for cross-country mobility but inferior to lighter mediums in sustained operations.[14] Production halted after the initial batch due to insurmountable logistical constraints: the M6's weight exceeded standard US railroad flatcar capacities (typically limited to 50-55 tons), requiring specialized reinforcements for bridges and overpasses, while its dimensions strained existing transport infrastructure designed for medium tanks.[11] By late 1942, field evaluations and combat data from North Africa demonstrated that the M4 Sherman's 30-ton frame, faster production rate (over 50,000 units versus the M6's 40), and comparable battlefield effectiveness against Axis armor negated the need for heavy tanks, as upgraded mediums with improved guns and sloped armor addressed protection gaps without sacrificing deployability.[10] The program was formally canceled in March 1944, with surviving vehicles repurposed for training gunners and engineers until scrapped postwar.[12] Testing revealed the M6's armor withstood 37mm and 50mm antitank rounds at typical combat ranges, validating heavy protection's viability for breakthrough roles, yet real-world trials exposed trade-offs: the twin-engine setup increased maintenance complexity, fuel consumption limited range to 100 miles, and overall mass hindered rapid maneuver, mirroring causal limitations in balancing invulnerability against operational tempo.[11] No M6 units deployed to combat, underscoring the US Army's prioritization of scalable, transportable designs amid industrial demands for quantity over experimental heavies, a decision corroborated by postwar analyses of Allied armored doctrine favoring medium tanks for combined-arms flexibility.[10]Guns and ordnance
The M6 37 mm gun was a United States tank cannon variant of the 37 mm M3 anti-tank gun, featuring a longer barrel (L/56) and semi-automatic breech for improved velocity and rate of fire in armored vehicles.[15] It fired the M51A2 armor-piercing projectile at a muzzle velocity of approximately 2,600 ft/s (790 m/s), achieving penetration of up to 36 mm of rolled homogeneous armor at 500 m (about 550 yards) at 0° obliquity.[15] Effective anti-tank range was limited to around 500 yards due to trajectory drop and accuracy constraints under combat conditions, with maximum ballistic range exceeding 6 km but irrelevant for armor engagement.[16] Early deployment in vehicles like the M3 Stuart light tank demonstrated initial success against thinly armored Axis vehicles in 1941–1942, such as Italian M13/40s and early Panzer IIIs with 30–50 mm flat plates.[17] However, by mid-1943, upgraded German tanks like the Panzer IV Ausf. H (80 mm frontal armor, often sloped at 30–50°) and Panthers (with 80 mm at 55° slope, yielding effective thickness over 140 mm) rendered it obsolete, as kinetic penetrators rely on sectional density and velocity squared for energy transfer, but small-caliber projectiles lacked sufficient mass to defeat composite effective thicknesses beyond 50–60 mm even at point-blank range.[15] Ballistic testing confirmed failures against sloped plates, where the normalization angle exacerbates glancing impacts, prompting phase-out in favor of 75 mm and larger calibers by 1944.[17] The M6 75 mm gun, adapted from the T13E1 aircraft cannon, served as the primary armament for late-war light tanks like the M24 Chaffee, emphasizing high-velocity armor-piercing performance in a compact package.[18] It fired the M72 AP shell at 1,929 ft/s (588 m/s) muzzle velocity, with penetration of 91 mm at 500 yards (0°), dropping to 66 mm at 1,500 yards, though hyper-velocity variants like the T45 AP achieved up to 2,025 ft/s for marginal gains against heavier targets.[18] Recoil forces, exceeding 10,000 lb despite muzzle brakes, necessitated reinforced mounts and limited ammunition stowage to 48 rounds in mobile platforms, compromising sustained fire.[19] In European Theater operations from 1944–1945, the M6 75 mm proved effective in reconnaissance skirmishes against Panzer IVs and lighter StuG IIIs, where side/aspect shots exploited vulnerabilities below 60 mm effective thickness, but frontal engagements against Panthers required tungsten-core rounds (scarce post-1944) or flanking maneuvers, as standard steel AP rounds normalized insufficiently against 55° slopes yielding 140+ mm equivalents.[18] Historical ordnance reports highlighted no revolutionary impact due to caliber constraints in kinetic energy delivery—approximately 2.5 MJ for AP rounds versus 5+ MJ needed for consistent heavy armor defeat—leading to reliance on high-explosive roles or support from self-propelled 76 mm/90 mm guns.[19]| Gun Variant | Caliber | Muzzle Velocity (AP) | Penetration (500 yd, 0°) | Max Effective AT Range |
|---|---|---|---|---|
| M6 37 mm | 37 mm | 2,600 ft/s | 36 mm | 500 yd |
| M6 75 mm | 75 mm | 1,929 ft/s | 91 mm | 1,000 yd |