MG Panzernest

Tank bunkers might be a pain in the ass when infantry runs into them unprepared, but a tailor-made solution is something else. I give you, the MG Panzernest, or as the Red Army nicknamed it, "Crab":

"This armoured container is a machinegun nest. Height: 1.8 meters, average diameter: 1.6 meters. Armour near the firing port: 115 mm, in the lower part near the hatch: 35 mm, in the upper part: 45 mm. The firing port is placed in the narrowest part of the container and contains two openings, one for observation and one for the machinegun. The size of the firing port is 160 mm by 110 mm. The firing port can be closed completely from the inside with a steel door. The entrance hatch is on the opposite side form the firing port. A machinegun is mounted on a special mount, giving it 45 degrees of range.
Observation of the battlefield can be done through periscopes, which can be covered up. In order to install the container, a trench 0.8 meters deep is dug. After installation, the container is covered in dirt. In most cases, the container is invisible on 1:8000-1:10000 scale aerial photographs." - Types of German Field Fortifications, November 1943

MG Panzernest from the top and from the front

MG Panzernest from the front. This photo makes it very obvious why these things cannot be seen from the air.

Rear side of the MG Panzernest.

Machinegun mount.

Extracted MG Panzernest at a trophy exhibit in Moscow.

MG Panzernest in transit and before installation. The metal shell is carried upside-down and flipped into the trench.

Via dr-guillotin.

German Tank Bunkers

Rounding out my collection of Soviet tank turrets dug in for defensive purposes, here are some designs for German attempts at the same thing. These three light tank turret designs appear mostly identical: a relatively short turret ring with a wider fighting compartment beneath it. Ammunition storage is not shown, but presumably it would be placed along the walls of the compartment.

Dig In

What do you do when you have a ton of old tanks kicking around? If you're the Germans, you throw away the turret, and put a bigger gun on top. However, that approach means you still have half of an obsolete tank, with no spare parts for it. The Soviets had different ideas: bury them.

Not entirely, of course. Think about the parts of the tank that wear out the most: the engine, the tracks, the road wheels. A tank can be immobilized by broken parts, and waste a perfectly good gun in the process. If you have a bunch of broken or nearly broken tanks, might as well drop them off somewhere they can be useful. Also, dig them into the ground, since they're not going anywhere anyway.

The following photos show some more MS-1s. These are armed with 45 mm guns, and have their "tails" removed. They haven't been dug into the ground yet, but they are going to be.

Interestingly enough, not all MS-1s met their end in a ditch. This page lists 3 MS-1s as a part of the 150th Independent Tank Brigade as of February 26th, 1942. 

Here's a rare one. That's not just any tank dug into the ground. That's a T-46 tank! They were meant to replace the T-26, but never quite managed to. A lot of them also ended up as fortifications as their final role.

Pre-war light tanks weren't the only ones to end up in the ground. A letter from the GAZ factory to GABTU from 1942 talks about 379 hulls for obsolete T-40 and T-60 tanks, and states that 150 hulls are available to GABTU to use as pillboxes.

Of course, not only light tanks became obsolete. Another letter to GABTU, this time from a tank school, states: "The school has 4 T-35 tanks and 8 T-28 tanks, which, after long use and numerous repairs, have become unusable and cannot be restored with the resources of the school. I await your instructions regarding transfer of these tanks to the armoured train directorate in order to install them as weapons platforms or immobile gun batteries in fortified regions." This letter was sent in 1943, long after those tanks would have been useful in combat. Let's see how this turned out:

CAMD RF 38-11355-963

Instead of leaving the turret on and using the tank's cannon, this pillbox design simply re-uses the hull. 

Something similar was done with the KV-1S:

CAMD RF 38-11355-963

During the defense of Leningrad, everything that could shoot was used, including the experimental Kirov T-50 tank. A curio of the Winter War, the T-100-Z, contributed to the defense, but not in its entirety.

"Leningrad Front. A tank that became a pillbox. Photograph by special correspondent A. Kapustyanskiy."

The Soviets were far from the only ones to bury their old tanks. Here is a British Medium Mk III buried at Mersa Matruh.