Originally, the Ferdinand was a tank destroyer. Its purpose was to sit far back and shoot tanks that crest hills or appear on the horizon. Since its allied infantry separated it from the enemy, there was no need to have a hull machinegun, or a machinegun at all.

However, the thick armour of the Ferdinand made it really tempting to use as an assault gun, which fights in a much more close up and personal fashion. This was the manner in which it was used during the Battle of Kursk, at Ponyri. Due to the Ferdinand's inability to protect itself from infantry in close quarters, many vehicles were knocked out by infantrymen throwing Molotov cocktails or anti-tank grenades.

Since the Ferdinand was actually designed with a machinegun and then had it taken out, there was an obvious place to re-insert the machinegun during the modernization process to help it function in its new role.

However, the machinegun ball mount added a critical weakness. I don't have any trials results for an Elefant (the Soviets only tested the Ferdinand), but trials of the Tiger II included firing at the machinegun ball with a 152 mm shell. The impact formed a crack in the front armour and tore off the ball mount fixture. In a combat situation, at least the hull gunner, and likely the driver, would have been killed and the tank would have required a replacement of the upper front plate to be serviceable again.

The King Tiger is hardly the only tank to have such a weakness. For instance, here is a photo of an MG mount on the LT vz. 38 (Pz38(t)) that was knocked inwards by the detonation of an anti-tank grenade. Soviet tank hunter manuals pointed to machinegun balls as being vulnerable to bullets and Molotov cocktails.

However, having an extra machinegun attached to your tank was still desirable. One solution was a fixed machinegun mounted in the hull, fired by the driver. This solution was tried on Soviet KV-85, IS-1/2 tanks and on the T-50 Kirov factory prototype tank. Ginzburg was not a fan of this solution: "This is a completely useless item which cannot provide any kind of accuracy and turns a machinegun into a child's toy." Combat use of this solution proved Ginzburg's assessment correct, and subsequent IS series tanks no longer had a hull machinegun. That is, all except one. Puzzlingly, the IS-7 mounted a total of seven machineguns. In addition to reasonable coaxial machineguns and a remote controlled AA machinegun, two machineguns were affixed to the sides of the turret and two more on the hull. The tank never entered mass production, and if it did, it is likely that this number of machineguns would be reduced to drive down the high cost.

On Soviet medium tanks, the hull machinegun survived for longer and could still be found on the T-55. However, the T-62 lacks it, as do subsequent Soviet designs.

Sources:

• Y. Bakhurin Panzerjager Tiger (P) "Ferdinand"

• Report on Ballistics Trials of the Front of the Hull and Turret of the Tiger B Tank, Central Archive of the Ministry of Defense of the Russian Federation

• Vulnerable Areas of a German T-III Tank, Voyenizdat

• http://tankarchives.blogspot.ca/2013/07/t-50-kirov-factory.html

• N. Nevskiy A Titan Late for the War

The Ferdinand has no integral machine guns at all, but it also had poor visibility. The success of Soviet infantry against it on the northern flank of the Kursk battle created a specific problem that led to the redesign.

For most nations, the experience was the opposite. The British started the war designing tanks with front sub-turrets. This was a habit of several nations, and was a hangover from the First World War when tanks were used to over-run infantry positions. Other tanks like the T-35 were envisioned as fighting a ship-like battle, cruising around knocking out enemy positions and vehicles.

The reality of tank combat in 1939 and 1940 showed the new war was not like 1914-18, and that the small turrets were useless, filling with smoke and being too small for comfort, while complicating design and armour layout. There is a great story, possibly apocryphal, about the design of the KV-1 tank, when several proposals were presented to Stalin of tanks with multiple turrets, in wooden mock-up form. Stalin is supposed to have knocked the extra turrets off one design, asking, 'Why turn a tank into a department store?'. David Fletcher in his excellent book on British tank development, The Great Tank Scandal, cites the persistent use of small sub-turrets as an example of the disconnect between British tank designers and the men who had to use them.

So the hull machine gun became common as a sort of compromise.

By 1944 technology and tactics had advanced somewhat. All the major combatants were now able to co-ordinate their combat arms effectively, using infantry and artillery to support their tanks, and defend them from the sort of inconveniences that the hull machine gun might have been used on. At the same time, guns were becoming large enough that stowing enough ammunition became a real issue, when the British made the Sherman Firefly they promptly eliminated the hull MG, put the radio in the back of the turret, and parked the space full of 17 pounder rounds. Tanks were also becoming heavier, with bigger engines, and they therefore needed to carry more fuel.

Additionally, radios became small enough to fit in the turret and be operated easily by the commander: the job of 'radio operator/hull gunner' was becoming redundant, visibility better, and tanks were being equipped with small mortars for protection. There were also new anti-personnel rounds like canister coming into use.

In short, but 1945 keeping the hull gun required too many compromises for too little advantage.