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  • Battle of Okinawa 65 Years ago today — May 17, 1945

    Posted by Trent Telenko on May 17th, 2010 (All posts by )

    May 17, 1945

    On Okinawa, the US 6th Marine Division, part of US 3rd Amphibious Corps, continues assaulting Sugar Loaf hill have Japanese positions are heavily bombarded by aircraft, artillery and ships.

    Elements of US 1st Marine Division capture the western part of the Wana valley but fail to take the ridge.

    Units of the US 77th Division, part of US 24th Corps, make a surprise attack on Ishimmi Ridge, west of the village, and end up in positions exposed to Japanese fire.

    Campaign Background — Japanese Anti-tank Defense vs M4 Sherman

    A Destroyed M4 Sherman on Okinawa

    One of the keys to understanding the Okinawa campaign is that it was only the second Pacific Island campaign — Iwo Jima being the first — where the Japanese deployed a continuous ground defense with a anti-tank gun line and an integrated doctrine to separate American tanks and infantry. This gun line was based on a weapon able to defeat the front hull of the M4 Sherman, the Japanese 47mm type 01 anti tank gun. The Japanese also, for the first time in the Pacific War, systematically destroyed abandoned M4 Shermans every chance they got.

    The Japanese 47mm type 01 anti-tank was based on experience fighting Russian tanks at Nomonhan and with the design influence of captured Russian 45mm anti-tank guns. The 47mm diameter and 51 caliber long gun was designed to be pulled by both horse and truck, so it had pneumatic tires, but lacked shock absorbers seen on western guns of similar size. This limited the guns towing speed on paved roads, but made it lighter for man handling into poor terrain.

    The primary Sherman marks for the US Marine Corps at Okinawa were the M4A3 and M4A2. The M4A3 had a rolled homogeneous armor (RHA) welded steel hull and a 450 HP Ford eight cylinder gasoline engine. The M4A2 had a rolled homogeneous armor (RHA) welded steel hull and twin General Motors diesel engines providing 410 HP.

    The primary Sherman marks for the US Army at Okinawa were the M4 and M4A1 both of which which had a cast front hull and welded body or a fully cast hull respectively. Both had the original pre-WW2 400 HP radial aircraft engine that was responsible the height of the Sherman.

    Over 85% of the Shermans on Okinawa were armed with the 75 mm medium velocity gun with a few 105 mm howitzer armed Sherman assault guns in the medium tank companies (one each per company) and US Army headquarters company (three each) in each independent tank battalions (six total per battalion). The 713th Flame Thrower Tank battalion had 54 M4A1 tanks armed with flame throwers instead of 75mm and 105mm guns in it’s three medium tank companies and had three M4(105) in it’s headquarters company.

    Most M4 Sherman tanks (and all models in the Pacific theater) had turret front armor three inches (76 mm) thick with turret side armor two inches thick (50mm). Pre-June 1944 manufactured Shermans had a 2 inch (50mm) 56 degree hull front slope and later production Shermans had 2.5 inch (63mm) 47 degree hull front slope. The hull sides and rear of a M4 Sherman were 1.5 inches (38mm) thick.

    This is the type 01’s performance against 30 degree slope rolled homogeneous armor plate:

    A.P. Shot Mk.I ( Armor Piercing )
    Weight……Velocity
    1.4 kg……..823 m/s

    Range in meters/Penetration in millimeters
    100 m…500 m….1000 m….1500 m…2000 m
    76 mm…64 mm….53 mm…..42 mm….34 mm

    The 47mm could punch through the hull front slope of early production Shermans at at 800 yards and later model Shermans at at 500 yards. It could go through the turret side of any Pacific theater Sherman at 1,200 yards and through the side and rear hull at any range it’s telescopic sites could get a hit. (The smaller Japanese Type 98 37 mm gun — a license produced copy of a 37mm German anti-tank gun — could hole the side and rear hull of a Sherman out to 1,000 yards.)

    This same 47mm gun was used in the Japanese Type 97 Chi-Ha medium tank, which was used in the Leyte and Luzon, generated the following report to US Army troops, “The Most Effective Jap Tank” from Intelligence Bulletin, July 1945

    Recent combat reports indicate that the quality of the 47-mm armor-piercing, high-explosive projectile has been improved. Moreover, tests show that the 47-mm tank gun will penetrate the U.S. M4A3 at 500 yards or more. In combat, one U.S. M4A3 medium tank was hit six times with armor-piercing, high-explosive rounds from this gun, at an angle of impact of approximately 30 degrees. Five complete penetrations and one partial penetration resulted. The range, according to members of the U.S. tank crew, was approximately 150 to 200 yards.

    There was more to the Sherman versus 47 mm story than just that.

    It was reliably determined by WW2 armor expert Robert Livingston (published in the book “World War II Ballistics: Armor and Gunnery” with co-author Lorrin Bird in 2001) that a large proportion of US steel tank armor, both RHA and cast, produced prior to November 1943 were flawed to such an extent that Sherman armor resisted about 5% to 50% less than it should have, with a mean resistance around 85% of 1944 and 1945 armor plate.

    The US Army Ordnance decided to accept the lower ballistic quality of cast armor when manufacturing the M4A1 Sherman, relying on a little extra thickness and the rounded corners to make up for the essential weakness of the cast armor material. In exchange, it got a more easily mass produced tank hull that was very durable for long road marches and hard training. It was also more easily repaired after battle damage than welded hull Shermans, being less prone to cracks.

    The composite cast/welded M4 was a mass production design half way house between the fully cast M4A1 and the all welded hull M4A3.

    However, the net effect of these design choices was that the later versions of M4 and M4A1 Sherman were less well protected on the front hull than the later versions of RHA Shermans (AKA the M4A3). One tank unit in North West Europe which had both RHA and cast hull Shermans (the 743rd Tank Battalion) kept their cast hull tanks out of combat, a lesson they learned the hard way.

    The US Army in Northwest Europe chose the radial powered M4 and M4A1 as their “standard model” for the early fighting in Normandy, most of which were built in 1943. The failure of the cast armor on those tanks are what lead to complaints of WW2 veterans like Belton Cooper in his book Death Traps: The Survival of an American Armored Division in World War II.

    This is one of the few places where the lower US Military priority for weapons in the Pacific War helped to save the lives of American Marines.

     

    4 Responses to “Battle of Okinawa 65 Years ago today — May 17, 1945”

    1. Michael Kennedy Says:

      The US story on tanks in WWII is a bitter lesson. I have a copy of “Death Traps.” He points out that one tank unit in Normandy had a 600% loss rate. The Pershing tank was available for Normandy but the Army decided to go for numbers. Why the hell they didn’t copy the T 34 is a mystery but the Ordnance Corps has many mysteries, such as why the US did not use the BAR in WWI. It was such a wonderful weapon, they feared the Germans would capture and copy it. So they didn’t use it.

    2. Trent Telenko Says:

      Michael Kennedy,

      The villian of the piece was neither US Army Ordnance or General Geroge Patton.

      It was Head of US Army Ground Forces General Lesley McNair.

      See the following:

      http://en.wikipedia.org/wiki/M26_Pershing

      Tank historians who have researched the original military documents such as Richard P. Hunnicutt, George Forty and Steven Zaloga have generally agreed that the main cause of the delay in production of the M26 was opposition to the tank from Army Ground Forces, headed by General Lesley McNair.[31][32] Zaloga in particular has identified several specific factors that led both to the delay of the M26 program and limited improvements in the firepower of the M4:

      1. McNair, who was an artillery officer by trade, had promulgated the “tank destroyer doctrine” in the U.S. Army. In this doctrine, tanks were primarily for infantry support and exploitation of breakthroughs. Enemy tanks were supposed to be dealt with by the tank destroyer forces, which were composed of lightly armored but relatively fast vehicles carrying more powerful anti-tank guns, as well as towed versions of these anti-tank guns. Because of the tank destroyer doctrine, emphasis was placed only on improving the firepower of the tank destroyers, as there was a strong bias against developing a heavy tank to take on enemy tanks. For this same reason, improvement of the firepower of the M4 Sherman was limited only to the 76mm gun upgrade.[33]

      2. McNair established a “battle need” criteria for acquisition of weapons in order to make best use of America’s 3000 mile long supply line to Europe by preventing the introduction of weapons that would prove unnecessary, extravagant or unreliable on the battlefield. In his view, introduction of a new heavy tank had many problems in terms of transportation, supply, service, and reliability issues, and was not necessary in 1943 or early 1944. The problem of course was that tank development took time, and so the sudden appearance of a new tank threat could not be met quickly enough with such rigid criteria.[34]

      3. A sense of complacency fell upon those in charge of developing tanks in the U. S. Army which came about because the M4 Sherman in 1942 was superior to the most common German tanks—the Panzer III and early models of the Panzer IV. Even through most of 1943, the 75mm M4 Sherman was adequate against the great majority of German armor, although the widespread appearance of the German 7.5 cm KwK 40 during this time had led to a growing awareness that the M4 was becoming outgunned. There was simply not enough forward thinking to understand that there was an ongoing tank arms race and that the U.S. armored forces needed to anticipate future German tank threats. The Tiger I and Panther tanks that appeared in 1943 were seen in only very limited numbers by U.S. forces and thus were not considered as major threats.[35] The end result was that in 1943, the Ordnance Dept., lacking any guidance from the rest of the Army, concentrated its tank development efforts mainly on its pet project, the electrical transmission T23.[36] In contrast, in the German–Soviet conflict on the Eastern Front in 1943, a full-blown tank arms race was underway, with the Soviets responding to the German Tiger I and Panther Tank by starting development work on the T34/85 and IS-2 tanks.

      The most critical period was from mid-1943 through mid-1944, which was when the M26 could still have come to fruition in time for the Normandy invasion. During this time, development of the 90mm up-armored T26 prototype continued to proceed slowly due to disagreements within the U.S. Army about its future tank needs. The details of what exactly happened during this time vary by historian, but all agree that AGF was the main source of resistance that delayed production of the T26:

      [edit] Zaloga version
      In his 2008 book Armored Thunderbolt, Zaloga significantly revised an earlier version of this story which had appeared in his 2000 book M26/M46 Pershing Tank 1943–53. Unlike the earlier book, Armored Thunderbolt quotes from a much more extensive list of original documents from the Ordnance Dept., Army Ground Forces, Gen. McNair’s correspondence, and other sources, which appears to be the reason for the change. Zaloga’s current take on this episode is as follows:

      In September and October 1943, a series of discussions occurred over the issue of beginning production of the T26E1, which was advocated by the head of the Armored Force, Gen. Jacob Devers. Ordnance favored its pet project, the 76mm gun, electrical transmission T23. Input from theater commanders generally favored a 76mm gun medium tank such as the T23, and were against a heavy 90mm gun tank. Testing by the Armored Force at Fort Knox of the T23 had demonstrated reliability problems in the electrical transmission however, of which most army commanders were unaware. The new 76mm M1A1 gun approved for installation on the M4 Sherman seemed to be the answer that addressed concerns about firepower against the German tanks. However, all participants in the debate were completely unaware of the inadequacy of the 76mm gun against the Panther tank’s frontal armor. Ordnance, the Armored Force Board, and AGF had all failed to research the effectiveness of this gun against the new German tanks, which had already been encountered in combat.[37]

      Single prototype of 90mm gun T26 turret mounted on an M4A3 chassis.Gen. Lesley McNair had agreed to the production of the 76mm M4 Sherman, and he strongly opposed the additional production of the T26E1. In the fall of 1943, he wrote this letter to Devers, responding to the latter’s advocacy of the T26E1:

      The M4 tank, particularly the M4A3, has been widely hailed as the best tank on the battlefield today. There are indications that the enemy concurs in this view. Apparently, the M4 is an ideal combination of mobility, dependability, speed, protection, and firepower. Other than this particular request—which represents the British view—there has been no call from any theater for a 90mm tank gun. There appears to be no fear on the part of our forces of the German Mark VI (Tiger) tank… There can be no basis for the T26 tank other than the conception of a tank versus tank duel—which is believed unsound and unnecessary. Both British and American battle experience has demonstrated that the antitank gun in suitable number and disposed properly is the master of the tank. Any attempt to armor and gun tanks so as to outmatch antitank guns is foredoomed to failure… There is no indication that the 76mm antitank gun is inadequate against the German Mark VI (Tiger) tank.[38]

      Gen. Devers pressed on with his advocacy for the T26, going over McNair’s head to Gen. George Marshall, and on Dec. 16, 1943, Marshall overruled McNair and authorized the production of 250 T26E1 tanks. Then, in late December 1943, Devers was transferred to the Mediterranean, where he would eventually lead the invasion of Southern France with the Sixth Army Group. In his absence, further attempts were made to derail the T26 program, but continued support from Gen. Marshall and Eisenhower kept the production order alive. Testing and production of the T26E1 proceeded slowly, however, and the T26E1 did not begin full production until November 1944. These production models were designated as the T26E3.[39]

      A single prototype of a T26 turret mounted on an M4A3 chassis was built by Chrysler in the summer of 1944, but did not progress into production.[40]

      [edit] Hunnicutt version
      Ordnance requested production of 500 each of the T23, T25E1, and T26E1 in October 1943. The AGF objected to the 90mm gun of the tanks, whereas the Armored Force wanted the 90mm gun mounted in a Sherman tank chassis (see above). Gen. Devers, by now in London, cabled in a request for production of the T26E1. In January 1944, 250 T26E1s were authorized. Gen. Barnes of Ordnance continued to press for production of 1000 tanks. Most of Hunnicutt’s information was from Ordnance Dept. documents.[41]

      [edit] Forty version
      Ordnance recommended 1500 of the T26E1 be built. The Armored Force recommended only 500 be built. The AGF rejected the 90mm version of the tank, and wanted the 76mm gun to be mounted instead. Ordnance somehow managed to get production of the T26E1 started in November 1944. Forty primarily quoted from a postwar report from the Ordnance Dept.[42]

      [edit] Production
      Regardless of how it came about, production finally began in November 1944. Ten T26E3 tanks were produced that month at the Fisher Tank Arsenal, 30 in December, 70 in January 1945, and 132 in February. The Detroit Tank Arsenal also started production in March 1945, and the combined output was 194 tanks for that month. Production continued through the end of the war, and over 2000 were produced by the end of 1945.

      Following its introduction into combat in Europe, the T26E3 tanks were redesignated as the M26 in March 1945.[43]

    3. Joseph Somsel Says:

      Now, tell us why early WWII US torpedoes were so bad.

    4. Trent Telenko Says:

      For the same reason the British and German torpedos were bad at the beginning of World War II.

      We had not tested our torpedoes either realistically or enough before the war.

      Torpedoes were and still are expensive. There was this thing called the Great Depression going on at the time and bread lines got more votes in Congress.