Most mid-20th century tanks seem to have had a hull machine gunner position. With limited arcs of fire and restricted elevation (hence no AA capability), it seems like a fairly redundant weapon - especially as in most cases there was also a coaxial machine gun for anti-infantry use.
It also seems very wasteful of manpower: having a hull machine gunner means you need rations and logistical support for 5 people, not 4, for each tank - hardly ideal when you are trying to maintain a large mechanised force in the field.
Q1. What was the intended tactical purpose of the hull machine gun in the military thinking of the pre-WW2 era? What sort of tactical doctrine gave rise to tank designers thinking a hull machine gun would be necessary?
Q2. How often, and how effectively, were hull machine guns used in practice?
Q3. Did the hull machine gunner have other duties, besides manning the MG, that justified the cost and logistical burden of an additional crewman?
Q4. Why do hull machine gunners mostly disappear after WW2? Was this in response to wartime experiences showing hull MGs to be redundant, or due to other tactical or technological changes in the post-war era?
Many thanks.
I addressed your point 2 in this question here and I'll paste it below.
Machine guns were very important weapons on U.S. tanks, particularly when they were used to support friendly infantry.
German soldiers were often quite afraid of the effect of the M2 .50 caliber antiaircraft machine gun mounted on the Sherman tank, but it was by default placed in an awkward position through the entire production run, so much so that the soldier using it had to expose either his whole upper body or entire body to fire it, leaving him vulnerable to enemy fire. The ammunition capacity of the .50 caliber machine gun was limited, only 300 to 600 rounds, and many crews removed it, as they mostly faced little threat from enemy aircraft and it just got in the way, especially if not disassembled and secured.
Convinced of the effectiveness of the .50 caliber machine gun, in early 1945, several units of Patton's Third Army, along with other systematic modifications to their tanks, replaced the coaxial M1919A4 .30 caliber machine gun with a .50 caliber AN/M2 aircraft machine gun. This modification is easily visible in photographs. General Patton admired machine guns on tanks, but was particularly outspoken on other technical issues; General Bruce C. Clarke described Patton as "knowing less about tanks than any general officer he ever knew."
Towards the end of the war and after, an experimental commander's cupola (more accurately a powered secondary turret) that mounted two .50 caliber machine guns known as the T121 was tested, but nothing came of the proposal.
The .30 caliber coaxial and bow-mounted machine guns were more versatile weapons than the .50 caliber machine gun, and represented the weapons with the most number of individual rounds fired through them in essentially all tank units. The 740th Tank Battalion routinely expended over 50,000 rounds per day, and a single company of the 741st Tank Battalion shot 100,000 rounds during an engagement lasting a few hours.
Here are the ammunition expenditures of the 743rd Tank Battalion from June 6, 1944 to May 8, 1945;
Ammunition expenditure
| Abbreviated nomenclature | 6 June 1944 to 8 May 1945 |
|---|---|
| Cal. .30 Carbine | 54,300 |
| Cal. .30 M.G. AP & TR (4-1) | 1,412,550 |
| Cal. .45 TSMG, Ball | 138,100 |
| Cal. 50 MG AP & I & TR (2-2-1) | 18,265 |
| 37mm M63, HE, TR or AT | 1,776 |
| 37mm M51, APC, TR or AT | 395 |
| 37mm, Cannister [sic], TR or AT | 480 |
| ++81mm, HE (lt) | 7,413 |
| ++81mm, Smoke, WP | 330 |
| Grenades, hand, frag. | 962 |
| ++105mm How., M2, HE, w/fuze M48A1 | 4,633 |
| ++105mm How., Smoke, M60, WP | 241 |
| 75mm Gun, HE, Super, w/fuze M48 | 14,400 |
| 75mm Gun, APC | 5,646 |
| 75mm Gun, WP | 5,545 |
| 75mm Gun, Cannister [sic] | 1,708 |
| Grenade, Incendiary, M14 | 135 |
| Grenade, Smoke, M8, HC | 6 |
| Smoke, Mortar 2" | 731 |
| Rocket, AT, M6A1, HE | 30 |
| Grenade, Hand, Colored, yellow smoke | 25 |
| Rocket, HE, 4.5", M8 unfuzed | 1,656 |
| Fuze, M4A1, for rocket, HE, 4.5" M8 | 1,656 |
| 76mm Gun, HE, m48A1 fuzed | 1,815 |
| 76mm Gun, APC | 1,240 |
| 76mm Gun, WP, w/fixed fuze [sic] | 346 |
| 76mm HVAP | 25 |
| ++81mm Mortar, HE (H) | 160 |
++ 81mm and 105mm ammo have been supplied to the Mortar and Assault Gun platoons by the infantry and artillery. Those figures are not available.
The .30 caliber machine guns were useful for engaging targets that were not worth a main gun round, or engaging targets that were moving too fast, had gotten too close to the tank for the main gun to shoot (more important in the Pacific, where Japanese infantry resorted to attacking U.S. tanks with handheld weapons more often than not), or thanks to the well-oiled American logistical machine, anything that looked "off," especially during aggressive reconnaissance. The bow machine gun, with its handheld traverse, was particularly useful in this regard, but it had no real sighting device and the gunner needed to "walk" his shots to the target using tracers. The Sherman could by default carry 6,000 to 6,750 rounds of .30 caliber machine gun ammunition, and many units augmented this capacity by installing extra storage devices or carrying ammunition on the outside of the tank, doubling or even tripling the capacity.
Sources:
Hunnicutt, Richard P. Sherman: A History of the American Medium Tank. Novato: Presidio Press, 1978.
United States. United States Army. Action Against Enemy/After Action Report. By William E. Park, 1st Lt., 741st Tank Battalion, Commanding. s.l., s.n., 1944.
-- Action Against Enemy, Reports After/After Action Reports. By William D. Duncan, Lt. Col., Infantry, Commanding. s.l., s.n., 1945.
Yeide, Harry. Steel Victory: The Heroic Story of America's Independent Tank Battalions at War in Europe. New York: Ballantine Books, 2003.
In regards to point 3;
On the M4 Sherman, the commander exercised primary authority over the use of the radio (SCR-508, -528, or -538), with the loader also being trained in its use. When a command radio (SCR-506) was installed in the right front sponson, the bow machine gunner assisted the commander and loader in operating it. The radio of the M3 and M3A1 Stuart was located in the right front sponson, and operated by the bow machine gunner; when the M3A3, M5, and M5A1 arrived with a radio mounted in the turret like the Sherman, given its four-man crew, the commander operated it in addition to loading the 37 mm gun. A command radio was tended in a manner similar to the Sherman. The AN/VRC-3, basically a vehicle-mounted SCR-300 "walkie talkie" was installed in many light and medium tanks beginning in late 1944 and allowed infantry to talk to the crew of a "buttoned up" tank via a handset mounted on the outside of the tank, usually on the rear.
I can answer the question 4. The main reasons why hull/bow machine guns disappeared in the post war period are following:
Pre-war and early war tanks usually have relatively thin frontal armor plating but late and post war tanks had thickness of 70-80 mm and it only incresead with time. So it became simply impractical to install bow-mounted machineguns in tanks.
And the last reason was that 4-tank crew was simply more optimal in terms of space available inside the tank. Late WW2 tanks almost universally had guns with calibers above 75 mm and shells for such guns were quite bulky, so keeping a fifth crewman meant less ammunition for the main gun. It is not coincidental that so many late WW2 and early Cold war tanks had ammo racks (and sometimes additional fuel tanks) besides the driver position.