Last time around, I published the Armored Board’s understanding of what various nations understood to be the thinking necessary behind heavy tanks. The majority of the rest of the report covers concerns more specific to the US heavy tank program.
It continues:
Problems in Rail Movement.
1) One of the most critical factors in hauling the 70-ton heavy tank on American railroads is the width of the tank. Both the T29 and T30 heavy tanks, and the M26 medium tank, require a railroad flatcar which is at least 10 feet 4 inches wide. In addition, the overall width of the tank should not exceed 11 feet 1 inch; therefore, it is necessary to reduce the overall width by removing the skirts and fenders when the tank is loaded for rail shipment. When this is done, the tanks are reduced to a width of 11 feet 1 inch.
2) Of the 94,593 flat cars in the United States, only 3,247 or 3.4 percent have a capacity of 70 or more tons and are of sufficient width to carry the T29 and T30 heavy tanks. There are 12,122 railroad cars in the United States which have the capacity and width to carry the 43-ton M26 tank. Forty days were required to collect the flat cars necessary to ship a tank battalion, equipped with M26 tanks, from Fort Knox, Kentucky, to Camp Cambell, Kentucky, for the maneuvers held there in May 1948.
3) Although it is feasible to transport the T29 and T30 tanks by rail in the United States, the shipment of a large number would require very careful planning.
4) It has already been noted that Soviet rail lines are limited to a width clearance of 10 feet 11 inches and a weight limit of 66 tons; therefore, it can be seen that the T29 and T30 heavy tanks are too wide and heavy to be transported on Russian railroads.
5) Information obtained by conversation with officers now at this station who had railroad experience in the European theater of operations indicates that the railroads on the continent will transport the 70 ton tank although the width of the vehicle makes the problem difficult. However, there are no European flatcars which can take the weight of the tank. If either the T29 or the T30 tank is to be transported on European railroads, flat cars capable of taking the weight would have to be provided.
Problems in Water Transport.
1) Ships. The capacity of the boom on ordinary cargo carrying ships is 50 tons. Although there are a few ships which have a larger boom, there would be a problem of loading and unloading 70-ton tanks from ships. Probably this problem could be overcome by the use of railroad shore cranes.
2) Landing Craft. It appears that the LCT(8) (UK), the LSM (US), LST(2) (US), LSD (US) and the LST1153 (US) will take the 70-ton tank, the only question being whether the decks and ramps will withstand the concentrated load.
a) Designs of the 70-foot LCM have been prepared to meet an expected requirement for a craft which could accommodate a 70-ton tank, and from which the tank could fire while embarked. These designs provide a landing craft which is too large, and too heavy, for a “ship-borne” landing craft. They can be transported to the theater of operations loaded with tanks only in the LSD-type craft. Present LSD craft can accommodate either nine of these smaller craft, or three of the LCT type. It is reasonable to expect that when empty these craft can be deck loaded on an LST, and side-launched similarly to the LCT(5) and LCT(6). The distinctive feature of the 70-foot LCM is extensive sectionalizing (nine sections) to permit overland transportation via Army 45-ton Tank Transporter, Truck Trailer, M19, or the Truck, M26A1-Transporter M15A1 combination or similar assemblies. Powered by three Gray Marine Diesels, a speed of ten knots (Loaded) is expected. This craft is expected in 1950.
Views of the Armored School
1) There exists in the American Army a need for a mobile armored fighting vehicle weighing not more than 50 tons and capable of mounting weapons with the armor penetration capabilities prescribed in the WEBR for guns to be used in heavy tanks. All around (360 degree) traverse can be sacrificed to achieve this vehicle. Missions to be assigned to such vehicles include
a) Destruction of enemy armor
b) Furnish direct fire support to other elements of the infantry and armored divisions.
2) Assuming a battalion of heavy tanks (similar to T29 and T30) in TAS troops, the following problems are anticipated.
a) Administration: Adequate facilities for motor parks, hard standing, quarters for personnel etc are at Fort Knox.
b) Maintenance. Stalls in maintenance sheds are too small. The width of Heavy Tank T29 is 149-11/16 inches, while the width of the widest available maintenance stall is 144 inches. Existing sheds could be modified to satisfactorily house heavy tanks. No other maintenance problems are anticipated.
c) Roads and Bridges. All roads on the post now in use by the M26 tank will carry heavy tanks. Most bridges on the post will not take a 70-ton load. By-passes around most of these bridges are already being used by the M26 and lighter tanks. All other bridges necessary for movement of heavy tanks can be bypassed with the exception of the Bailey Bridge over Salt River. With the exception of the area North of Salt River, all tank training areas now in use by the M26 can be reached by heavy tanks.
d) Training Areas and Ranges. Training areas for heavy tanks are adequate and will pose no problems that are not already encountered in training with the M26. In the matter of ranges, both the 105mm and 155mm gun can be fired on all ranges now used by the 90mm Gun, M3. It is apparent, however, that a greater safety factor must be allowed on the flanks of the firing fan than is presently required because of the danger of greater deflection using the 105mm and 155mm guns, furthermore required ranges backing will be increased in the case of the 105mm gun.
Fire Power.
1) General. A detailed discussion of armament, ammunition, fire control equipment, and stowage in Heavy Tanks T29 and T30 is contained in separate reports listed in Appendix B. It is sufficient here to make clear the fact that both 105mm Gun, T5E2 (T29 tank) and 155mm Gun T7 (T30 tank) represent first efforts to adapt large caliber guns to tank turret mounting; and, because of ammunition weight and bulk, it has been necessary to employ separated projectile and propelling charge.
2) Performance.
a) Armor Piercing Ammunition. Rated penetration of 105mm Gun, T5E2 and 155mm Gun T7, firing present special ammunition is substantially equal and between 85 and 90 percent of the WDEBR requirement for the lighter gun mounting in the heavy tank. Performance of neither gun approaches the more severe requirement established in the equipment report for the heavy gun mounting in the development heavy tank. Perfection of sabot ammunition for these two guns would probably increase performance sufficiently to meet the so called light gun penetration requirement. The foregoing estimates are based on the assumption that tungsten cored ammunition will be available.
b) Shaped Charge Ammunition. Until the adverse effects of spin on the performance of shaped charge shell are overcome, neither of the two guns in question can be considered truly efficient when firing this type ammunition although the larger caliber gun is clearly superior. This statement is based on computated penetration estimates of from 5 to 6 inches of armor for the 105mm gun, and 8 to 9 inches for the 155mm gun. Provided that a practical means or design can be found to overcome the adverse effects of spin, then performance of both guns against an unprotected, armor target will be of the order of 11 inches and 17 inches respectively.
c) Squash Head or Plastic Charge Ammunition. Performance with this type ammunition is almost directly related to caliber of shell. Tests so far made, although not conclusive, would indicate that both guns firing plastic charge shell would be able to defeat (By scabbing the rear side) armor plate of at least caliber thickness, even at obliquities of 40 to 60 degrees.
d) Concrete Piercing Ammunition. In the attack of high grade, reinforced concrete at ranges of less than 500 yards the 155mm gun firing either armor piercing ammunition or high explosive ammunition with CP fuze has a slight edge over the 105mm gun firing armor piercing ammunition. At ranges of about 2,000 yards this difference almost completely disappears. (As a matter of general interest, these figures are 5 feet for the 155mm gun at 500 yards compared with 4.5 feet for the 105mm gun; at 2,000 yards the rated penetrations are 4.2 and 4.1 feet respectively.)
e) High Explosive Ammunition. The present high explosive shell (HE, M101) for 155mm Gun, T7, carries about four times as much expolosive filler (15.5 pounds) as does Shell, HE, T30E1 (equivalent of M38) for 105mm Gun, T5E2 and is therefore distinctly superior in fragmentation and demolition effect. The shell for the 105mm gun is essentially the same as the high velocity antiaircraft shell and therefore can be improved a great deal if redesigned for the present muzzle velocity of 2,500fps. This, then, may be interpreted to mean that the present inequality between the 105mm and 155 high explosive rounds is not final and may be reduced on a relative basis.
3) Discussion.
a) General. The lack of specific ammunition performance data combined with the fact that testing under closely related service test projects (Projects 1325 and 1326) has not been completed makes it unwise to attempt at this time a final selection or rejection of either Heavy Tank, T29 or Heavy Tank T30 so far as fire power is concerned. However, they both fail to meet certain of the established requirements for performance and must therefore be considered as deficient in this respect.
b) Stowage; Service of the Piece. The Heavy Tank, T29, stows 63 rounds of ammunition compared with 40 rounds in the Heavy Tank, T30. Rate of fire with either installation as presently constituted is likely to be unacceptably low for a direct fire weapon intended to engage the enemy’s heaviest, most powerfully armed and armored vehicles.
c) Defeat of Heavy Tanks. Neither of the two guns under consideration can be expected to defeat the front plate of the Mark VI (Tiger Royal) or Josef Stalin 3 at any reasonable range irrespective of the directness of angle of attack. The 3-inch (plus) hull side of the Mark VI inclined at only 25 degrees is overmatched by both projectiles (Standard) and should be vulnerable throughout a fairly wide choice of angle and range of attack. The hull side (upper) of Josef Stalin 3 is 90mm inclined at 45 degrees and is therefore considerably less vulnerable to the two guns in question respecting both angle of attack and range. Hull sides (Lower) are of the order of 3 inches placed vertically on both Mark VI and Josef Stalin 3, hence these particular areas present no problem to either gun. The turret front and sides of the Mark VI turret are about 7.5 and 3.5 inches basis respectively. Thus either gun can expect to defeat the turret side even at fairly long range; however, it is estimated that only at ranges of the order of 1,000 yards or less can the main armament of Heavy Tanks T29 and T30 consistently defeat the turret front of Mark VI. The 200mm turret front of Josef Stalin 3 is well rounded and presents a very difficult target for either gun. The turret sides, if 200mm basis (or equivalent thickness), would be equally as difficult to defeat as the turret front. If the turret sides are an actual thickness of 200mm and are inclined at what appears to be about 45 degrees with an overall rounded effect then the task of penetrating is not likely of attainment by either gun under consideration irrespective of range or angle of attack. Most of the target plates just discussed can be defeated by an efficient 155mm plastic charge shell irrespective of range or angle of impact; similarly, most of them can (theoretically) be defeated by a 155mm HEAT or simple shaped charge round. If the adverse effect of spin can be overcome then 105mm caliber would be sufficient to defeat the most heavily armored known vehicle. The 105mm gun firing plastic charge and/or unimproved HEAT would be notable less effective on the heavier plates.
Eventually, of course, guns caught up.
d) Attack of concrete; demolition and fragmentation effect. Demolition and fragmentation effect of 155m shell is clearly superior to that of 105mm shell. There is, however, little difference in concrete penetrating ability between the armor piercing rounds for each. A comparative rading of the concrete penetrating ability of the 105mm high explosive round equipped with CP fuse is not available.
4) Summary
a) all around performance of the 155m Gun, T7, in Heavy Tank T30 with respect to terminal effect appears to be generally superior to that of the 105mm Gun, T5E2 on Heavy Tank, T29; however, this superiority is, for the most part, restricted to high explosive shell effectiveness and to a potential advantage whose realization is continegnt upon employment of shaped charge and plastic charge principle in shells not currently available. There is essentially no notable difference in penetrating ability for the two guns firing HVAP ammunition at ranges of 2,000 yards. The 155mm gun possesses an advantage in muzzle energy with the standard AP round in the ratio of almost 8-5; however, since energy density is a better penetration criterion than total energy in most cases the apparent superiority of the larger projectile tends to be reduced. There is, however, a distinct advantage inherent in the projectile with larger diameter. In order to defeat very hard, thick plates at great obliquities, it has been found that a projectile with diameter which matches or overmatches plate thickness is nearly always required.
b) considering not only terminal performance but vehicular stowage capacity, potential rates of fire, and the higher probability of hitting the target due to high velocity, it appears that the 105mm equipped Heavy Tank T29 is superior to the Heavy Tank, T30 as far as tactical consideration of firepower is concerned.
c) Unless and until more lethal ammunition is developed for conventional guns, attainment of the high penetration requirement for the heavy tank gun prescribed in WDEBR (10 inches @ 30 degrees at 4,000 yards) is clearly doubtful with a gun which can be satisfactorily mounted and served in a practicable turreted vehicle.
d) The final outcome of current armament and fire control tests on the two tanks in question will give a good indication of limits to tank armament caliber and potential suitable mounting in tank turrets with -360 degree traverse.
Armor Protection.
The armor protection afforded by Heavy Tanks T29 and T30 is unquestionably less than that required of the heavy tank in specifications of the War Department Equipment Board Report (i.e. “heavily armored with front armor capable of capable of withstanding any probable anti-tank fire”. Reliable terminal ballistic performance data on the most recently identified potential enemy tank and anti-tank artillery materiel are not available. Data on older wartime gun models are fragmentary and largely pure estimates. It, therefore, appears that specific prediction which can be made by the Board under such circumstances will be of questionable value and may be even misleading. After evaluating available information including limited data on the performance of comparable US guns, it appears that the Heavy Tanks T29 and T30 are vulnerable to the potential enemy’s medium and heavy, tank and antitank artillery with considerable latitude as to range, angle of target presentation, and area of attack on the tank. In general, the hull affords better protection than the turret. However, in neither case is all-over protection equal to that afforded by Mark VI (Royal Tiger) or Josef Stalin 3, both tanks of somewhat lesser total weight; nor is protection afforded by the tanks in question equal to that of the US Heavy Tank T32 or T32E1. Every effort should be made to improve on the lines (angularity) of the Heavy Tanks T29 and T30 since in each instance their massive projections (silhouette) present to the enemy gunner a large target especially through the turret. It may then be concluded that these two tanks are underarmored for the heavy tank class indicated by development trends in potential enemy equipment.
Overall, the report made three recommendations.
1) Heavy Tanks T29 and T30 be considered unsatisfactory in their present stage of development.
2) Heavy tank development, including Heavy Tanks T29 and T30 continue with a priority below that accorded the medium tank and the vehicle mentioned in 3) below until an acceptable item is obtained.
3) Concurrently there be developed a tank which sacrifices all around traverse for portability, mobility and protection. It should not exceed 50 tons, should mount the best possible armor piercing weapon, and have at least the armor protection of the medium tank.
Here’s the TL,DR version.
The US Army wanted a tank which I’m not sure even they believed was entirely possible with the level of technology then available. There was also a level of contradiction: They wanted a gun which was capable of defeating all likely armor possible of being placed onto a tank while, at the same time, wanting sufficient armor to be proof against any gun. The armor team and the gun team must have had some interesting discussions. More importantly, note the amount of emphasis placed on strategic and operational mobility. Getting a tank to move about the battlefield doesn’t seem to have placed anywhere near as many restrictions on the design, or taken as many processing cycles, as being able to get it to the battlefield in the first place. Granted, it was not wartime, but six weeks to collect enough railway rolling stock to move a battalion of medium tanks is a significant amount of time. Getting the rarer heavy capacity flatcars would have taken even longer. There is little surprise that Transportation and Engineering corps usually placed objections to heavy tanks when they came up.
It is interesting to note the comparative value of the T29 to the T30. T30 provided no particular improvement in anti-armor lethality, which seems to have been the driving force behind the heavy-tank criterion, and did better at dealing with bunkers and infantry at the cost of a very reduced rate of fire and ammunition capacity. Did the merits of the one bigger bang outweigh the overall weight-of-shell per minute that the two types of tank could fire? Perhaps T34 would prove to be the compromise blend. After all, when the US finally did decide to build a heavy tank in the M103, they went with the 120mm.
As a related reminder, this article from about two years ago, http://worldoftanks.com/en/news/21/The_Chieftains_Hatch_T29T30/ , also went over the T29/T30 testing.
Bob for the forum thread.
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