Interesting notes on US tank destroyer secondary roles

[Andras]

From Seek, Strike, and Destroy: U.S. Army Tank Destroyer Doctrine in World War II, Dr. Christopher R. Gabel found at the US Army Command and General Staff College online library.

[formatting is a little off because it's a text clip from a PDF file, paragraph spacing is mine]

Although tank destroyer doctrine held little utility in North Africa and Italy, this is not to suggest that the tank destroyers themselves were useless.

In addition to contributing significantly to frontline antitank firepower, tank destroyer battalions, on their own, developed new missions that were not to be found in FM 13-5. The battalion that pioneered the development of secondary missions was apparently the 776th, commanded by Lieutenant Colonel James P. Barney.

Barney, like many other tank destroyer officers,
was an artilleryman. (Of the traditional arms, Field Artillery felt the closest kinship to the fledgling tank destroyers.) As a gunner, his instincts rebelled
at the thought of leaving the battalion’s thirty-six tubes idle in the absence of an enemy tank threat.

To provide employment for his battalion, Barney worked out techniques and procedures for using tank destroyers as indirect- fire artillery in support of the howitzers of division artillery. Other battalions were quick to emulate the 776th.

Barney divided his three companies into two six-gun batteries, rather than the three four-gun platoons specified in the tables of organization. This restructuring freed some platoon officers to act as observers and pro-
duced a battery with approximately the same firepower as a standard battery of four 105-mm howitzers He then placed each company in support of an artillery battalion. The tank destroyer companies commonly operated their own fire direction centers but, lacking sophisticated equipment, relied on division artillery to help with surveys.

The thirty-six three-inch guns mounted on Barney’s M-10s equaled the number of tubes found in three field artillery battalions. Moreover, the three-inch weapons complemented the 105-mm howitzers nicely. They could
reach out to fourteen thousand yards-four thousand yards farther than the 105-mm. The three-inch weapon was very accurate, and its shell arrived on target with little warning. The burst radius of the three-inch shell was about equal to that of the 105-mm, but its instantaneous burst reduced the amount of cratering sustained by roads in the path of friendly forces.

Moreover, three-inch rounds were cheaper and, being smaller, easier to transport than 105-mm shells. These qualities made the three-inch tank destroyer gun
ideal for long-range harassment and interdiction, freeing the artillery’s howitzers for close-range missions requiring heavier metal.

The fully tracked M-10 was itself a good gun mount. The tank destroyers could displace and occupy new positions with a minimum of site preparation. Especially when dug in and provided with an improvised turret cover, the M-10 was relatively immune to counterbattery fire. Moreover, the M-18 sought out reverse slopes as artillery positions (to supplement the elevation of the gun), leaving the level ground for towed artillery.

In Italy, it was discovered that the M-10 could tow a 105-mm howitzer during displacements, freeing the howitzer’s prime mover to haul ammunition and supplies. But the employment of tank destroyers as reinforcing artillery was not without its drawbacks. Constant firing wore out the high-velocity tubes
relatively quickly. Although tank destroyers maintained a basic load of antitank ammunition even when serving as artillery, the secondary mission, nonetheless, interfered with their ability to train for the antitank role. Some battalions split their companies between artillery and antitank missions to maintain a degree of antitank readiness.

These drawbacks notwithstanding, battalion commanders agreed that morale improved when tank destroyers were employed in meaningful missions all the time, be they antitank or artillery.

Barney’s 776th Tank Destroyer Battalion discovered that when placed well forward in the lines, tank destroyers could fulfill another valuable secondary mission-that of direct-support artillery. Late in the Tunisian campaign, the 776th found itsellf in support of an attacking tank unit. Prior to the armored assault, the tank destroyers methodically shot up all potential German’ defensive positions with their powerful three-inch guns. The
tanks attacked without loss to antitank guns and discovered that the German defenses had been thoroughly demolished by the destroyers’ fire.

The 776th built upon this experience and developed a leapfrog technique that allowed the tank destroyers to maintain continuous direct-fire support for advancing friendly elements. The direct-fire mission was especially important in Italy, where tank destroyers provided covering fire for tanks that, being better armored, closed with and destroyed enemy positions impeding the advance of the foot soldiers. Thus, tank destroyers supported tanks, and tanks supported infantry.
During the September 1944 assault on the Gothic Line, specially trained tank destroyer gunners supported the advance by placing rounds through the small gun embrasures of German pillboxes at a range of fifteen hundred yards.

Even when openings could not be hit, the high-velocity rounds were quite effective against concrete fortifications. Tank destroyers were so valuable as armored self-propelled assault guns that one battalion in Italy functioned exclusively in the direct-support role for four months.

[Lynx7725]

While the effectiveness of the Tank Destroyers in this role is surprising, the usage of it is not; US forces routinely utilized tanks (and IIRC TDs) in indirect fire support, although admittedly photos of M4s with a garbage pile of discarded 75mm rounds and shipping containers around it is more common.

[protevangelium]

That's an interesting snippet. Compare that with the role of the M12 155mm SPG as a direct-fire weapon, especially during the battle for Metz! Stephen Ambrose seemed to have a love for this gun, as he mentions it at least twice in Citizen Soldiers.

[fifleche]

I have read the same about long-barreled german tanks.

Anyone has an idea if the brits did this too? I doubt russia would have done so, altho the IS gun is an artillery piece...