The granddaddy of heavy calibre machine guns

The British introduced armoured vehicles with internal combustion engine ("tanks") into land warfare in 1916 on the battlefields of the Western Front trench war; the First World War as most imagine it.

Germany had addressed the same problems with more infantry and artillery innovations instead of with tanks. Its anti-tank defences employed many means, but they weren't fully satisfactory. The British simply concentrated too many tanks on a too narrow front and were thus able to overwhelm the defenders on the battlefield if they didn't blunder (the exploitation of this breakthroughw as still a problem in search of a solution).

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The tanks of WWI were very imperfect, and one of their imperfections was a very weak armour plating. Their armour was barely able to withstand hand grenade explosions and steel-core bullets fired from normal machine guns (7.92x57mm AP).

One of the few German development programs against this new problem was the development of the granddaddy of all heavy calibre machine guns: The Tank und Flieger (TuF, tank and aircraft) machine gun. It was basically an enlarged Maxim machine gun with a more powerful cartridge that offered the necessary penetration power to turn tanks into swiss cheese and it had the necessary external ballistic performance to serve as air defence in a good radius.

fully automatic, water-cooled, Maxim action
calibre 13x92mmSR (semi rimmed)
approx. 300 rpm cyclic
penetration of 24 mm steel at 100 m
(90° / 120-150 kg/mm2 strength)
penetration of 18 mm steel at 300 m
(90° / 120-150 kg/mm2 strength)
(common tank armour of that time was 6-16 mm)

The first prototype was demonstrated on July 1918, 50 pre-series copies were ordered in August 1918. The army didn't get any copies any more because the war ended shortly after.

This kind of firepower would have been badly needed in 1919 if the Western Entente powers had realised their plans for many thousands of new tanks and ground attack aircraft.

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Such heavy calibre machine guns proved to be rather useless as anti-air and anti-tank weapons in WW2 and were instead used for air combat and ground/ground fires.

Their weak performance in the air defence during WW2 should be seen in context of the vastly increased aircraft speeds and aircraft firepower. The .50cal machine guns used by the U.S. Navy proved to be near-useless for the protection of destroyers and capital ships in part because Imperial Japanese Navy aircraft released their torpedoes and bombs outside of the effective range of .50cal weapons.

The poor performance against tanks was on the other hand a product of a revolution in tank technology that occurred in the 1930's. WWI tanks were bulletproof, but most WW2 tanks were shell-proof. Even early WW2 tanks weren't well protected - armour thicknesses as up to 30 mm weren't uncommon. Such an armour was able to defeat anything up to calibre 25mm, but rarely anything better. The famous T-34 shock was in part the shock cause by the T-34's shell-proof front and side armour. It was pre-dated by British Mathilda tanks and French Char B-1(bis) tanks, both of which were shell-proofed as well. The Germans had still defeated these in battle and didn't expect similar or better armour in the Soviet Union.
Weak anti-tank weapons such as the M2HB and anti-tank rifles were still useful against scouting vehicles and protected auxiliary vehicles such as the half tracks, of course.

(Surviving TuF example in the WTS museum, Germany.
photo courtesy of milpic.de, description detail here)

The TuF (and the comparable M2HB) would have been a useful heavy machine gun for the "heavy" companies of infantry battalions during the 20's and 30's - a period that luckily experienced little modern warfare. This is probably the reason why these heavy calibre machine guns never rose to fame as anti-tank and anti-aircraft weapons, but as air combat and vehicle-mounted ground combat weapons.

By the way; the same 13mm calibre cartridge was also used for a 13mm Tankgewehr in 1918, the granddaddy of all anti-material rifles (a.k.a. anti-tank rifles)!

Sven Ortmann

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