While we’re talking tanks — we’ve recently covered armor protection in WWII and rates of turret traverse, and the technical considerations that went into them — let’s talk a little about secondary armament.
Most tanks have had, since the 1930s, a main gun that’s primarily designed to fire anti-tank ammunition, but is also capable of firing high-explosive general-purpose shells, and secondary armament of machine guns. This has come to be accepted as the norm, but it wasn’t always so.
The first tanks deployed by the British Army in 1915-16 were laid out differently from modern tanks. Their automotive equipment (a Ricardo engine and drivetrain) was contained with most of the crew between the tracks, which wrapped around the periphery of the lozenge-shaped tank. Armament was exiled to sponsons which hung off the sides of the tank, outboard of the tracks. These tanks came in “male” and “female” versions, which was defined by their armament. The “male” tank had a small artillery piece in the front of each sponson, and a machine gun in the rear; the “females” had machine-guns all around and were intended to provide support against close-in infantry for the male tanks.
Later, Germany’s first real production tank, the Panzer I, was armed only with machine guns (initially, 2 x MG.13, later 1 x MG.34), as were some inter-war light tanks of Britain, America and Russia, and even the first version of the US M2 Medium Tank, America’s most important inter-war tank. But at the war’s outbreak, and through to war’s end, most tanks were conceptually similar to modern tank: a main gun, a coaxial machine gun that shared the main gun’s aiming systems, and one or more guns atop the turret for antiaircraft use. (One thing WWII tanks almost all did have, which now almost no tanks have, is a bow machine gun aimed by a crewman sitting beside the driver. This gun station was deleted from postwar tanks worldwide).
Secondary Armament Trends as Illustrated by the US Example
The trend in the 1930s and 1940s was for fewer machine guns. This photo from Aberdeen Proving Ground’s museum shows what we believe to be one of only two surviving M2 Medium Tanks (an M2A1). Apart from its primitive, riveted hull of face-hardened armor (a weakness that would persist into the early models of its replacement, the M3), you can see four of its seven fixed machine gun positions in this view.
Each sponson, at the four corners of the fighting compartment, hosted an M1919 Browning machine gun. In addition, two more MGs were fixed to fire forward through the glacis — you see their places left and right of the national insignia. A co-ax in the turret brought the 1919 count to seven; with two AA machine guns added, which could be on the turret or firing through roof hatches in the main-hull fighting compartment, this late-1930s monstrosity could have nine MGs on board, plus the puny 37mm (1.5″) main gun.
Here’s an interior shot (from this page) of the back of the other surviving M2A1’s fighting compartment, showing the two aft sponson MGs, and one AA MG. These rear guns had a unique special-purpose application on the M2: they could be fired at 45-degree “bullet deflectors” above and behind the rear fenders, and would deflect the stream of bullets down — this was to help the tank to kill any infantry it rolled over in trenches.
Seven to nine machine guns are a lot of secondary armament, and one of the problems with that is that it required a large crew to run all the guns. The M2 required a crew of at least 6, although internet sources are all over the ballpark with claims from 4 to 9.
The M3 that replaced it (called “Grant” and “Lee” by the British, depending on which turret the tank had) had more firepower (a 75mm gun based on the old “French 75″ that was the cornerstone of American gunnery, set in a right-side superstructure sponson) and fewer machine guns (only 2, a co-ax in the 37mm turret and an MG in a small commander’s turret in US-turret versions or an AA/GP flexible gun with the British turret). It got by with a crew of 6 (UK) or 7 (US, adding a Radio Operator). And the M4, which had replaced the M3 by early 1944, went to war with only 3 machine guns (bow, co-ax, and AA/GP atop the turret) and a crew of 5.
There were real benefits to a smaller crew. These were primarily logistical. If you could save one man from a crew, you could get a bonus 16-20% more crews from the same number of recruits, and have to supply proportionally less water, food, and all items for which headcount is a cost driver, to any given number of tanks or tank units. But there is also a benefit in that a smaller crew makes for easier intracrew communication and coordination.
The colorful (if over-compressed in the archive.org copy) summer, 1941 propaganda video, The Tanks Are Coming, celebrates American tanks, and includes the M2 Medium; M2, and M3, Light tanks; and White armored scout cars. (Unfortunately, it’s too big a file to embed here, so we’ll just send you to the Archive.org page).
Note at the 8 minute mark some of the simulators used to train tank gunners, including a sort of air-driven tommy gun and a “wobble platform” designed to make gunners proficient in firing the main armament from a tank moving cross-country. Later in the video, they show an incredible new vehicle, the “Blitz Buggy” — we’ve come to know it in the decades since as the Jeep!
You can see the M3 tank (in the version the British called the “Lee”) in the 1943 movie Sahara with Humphrey Bogart.
The Importance of Secondary Armament in Combat
While much of tank training and gunnery tables assume tank-versus-tank combat, much of armor strategy involves hitting the enemy with your tanks where his tanks are not. That’s where secondary armament comes to the fore. Machine guns are necessary in this tank-vs-enemy-logistical-trains and rear-echelon-units warfare; they are what takes a tank breakthrough of the enemy’s hard-shell combat line and turn it into a rout.
The next most important use of the secondary armament is in tank-vs-tank or combined arms combat, in keeping hunter-killer groups of infantry of one’s own and one’s unit’s tanks. In the Pacific, for example, both Japanese and American tanks were more likely to be lost to infantry attacks than to tanks or dedicated anti-tank artillery. Infantry methods of tank-killing ranged from prying a hatch open and shooting the crew to, later in the war, specially developed infantry anti-tank weapons with hollow-charge warheads.
Finally, the armor branch, perhaps because they are a more-technical crowd, less shy of innovation than the tradition-bound infantry, have been a proving ground for new machine-gun concepts over the years. Some, like the US M73 and M219, were complete failures, as was the attempt to adapt the M60 to tank use. But the M1 tank’s adoption of the superior M240 machine gun laid the groundwork for that gun to replace the M60 for the infantry, for which blessing every grunt ought to buy the next tanker he meets a beer.