Myths about the role, and perceived anti-tank capability of the M4 Medium, continue to be pervasive. The idea that US tanks were not expected to be able to deal with any tanks that they may happen to come across just won’t die, and is probably a reflection of the name of the US Tank Destroyer branch which is confusing to those who don’t understand the doctrinal function of the TD. See the Can Openers article for a slightly more in-depth look.
We know that the idea of adding the 76mm to the M4 pre-dates the introduction of the German cats. We also know that even without the 76mm the US Army as a whole wasn’t proven to be at any particular disadvantage. See US Guns, German Armor Part 2 . What is less well known, however, is the idea of totally replacing the 75mm tank was well entrenched long before the Normandy landings. In a nutshell, the long term plan was always to have two types of M4 in production: 76mm and 105mm.
The story starts even before of the US’s entry into the war, in Sept of 1941, when they decided that they wanted to fit the 105mm and 3” guns to the M4. The latter was a tad heavy, so they went and developed the lighter-weight 76mm which was in testing by the following August. So confident were they that the 76mm would work that by mid August 1942, the 76mm tank was classified as a substitute standard (i.e. can be issued in place of 75mm tanks), long before tests were completed.
These initial tests basically involved fitting a 76mm gun to a basic M4, and was deemed a stop-gap measure. The Armored Force, however, wasn’t overly impressed by the cramped and make-shift creation, and rejected it outright, saying that the “[g]un mount and the turret arrangement is unsatisfactory principally for the reason that the gun mount employed in the quick fix turret does not provlde adequate space for the installation of slghting telescopes of suitable size and power to develop the full potential capabilities of the 76mrn gun.”
There were other minor deficiencies noted in the report of April 1943, such as inadequate recoil mechanism (Fixed with stronger recoil piston rods) or an excessively weak elevation gear which made accurate laying impossible and precluded the completion of accuracy tests, or the travel lock blocking the driver’s vision. Small stuff. However, Armored Force did conclude that development of the 76mm gun for the M4 be ‘continued and expedited.’ Another recommendation was for inclusion of “the latest developments in ammunition stowage to prevent ammunition fires in tank”
Note that this is from the Armored Force Board report, not Ordnance Branch. It wasn’t just Ordnance pushing for the development of the 76mm M4, and it wasn’t Armored Force refusing to accept any need for the 76mm armed M4 until the lessons of Normandy beat it into them, contrary to popular belief. Incidentally, OCM 19984 of March 1943 also indicated that the Tank Destroyer Board was to test the M4A1 76mm, but I haven’t discovered any reports from that test or indications that the TD Board ever carried them out (Granted, I haven’t specifically looked for them either)
The response was fairly swift. By 03MAY43, the Ordnance Committee had revoked the substitute standard of the M4A1 76mm, and officially initiated development of the M4E6 series of tanks.
Ordnance were ahead of the game, though. General Barnes had verbally approved the idea of taking the turret of the T20 tank back in March, and putting it onto the M4. The E6, however, was going to be more than just a firepower upgrade, it was more of a mid-life tank design refinement. It would incorporate wet ammunition racks, a new front contour, thicker hull armour, new hatch designs, oil cooler design, relocated generator, and a slew of other enhancements.