The Medium Mark I replaced some of the Mark V heavy tanks; together with its successor, the slightly improved Vickers Medium Mark II, it served in the Royal Tank Regiments, being the first type of the in total 200 tanks to be phased out in 1938.
The Medium Mark I was the first tank to see "mass" production since the last of the ten Char 2C's had been finished in 1921. Indeed, as of the next tank, the Renault NC27, only about thirty were built, the British Mediums represented most of the world tank production during the Twenties. They never fired a shot in anger and their performance in a real battle can only be speculated upon but as the only modern tanks in existence in the decade after the First World War they provided the British with a unique opportunity to test the many new ideas about mechanised warfare using real operational units. The knowledge thus gained would prove invaluable in the Second World War.
| Vickers Medium Mark I | |
|---|---|
| Type | Medium tank |
| Place of origin |  United Kingdom |
| Production history | |
| Manufacturer | Vickers |
| Specifications | |
| Weight | 11.7 tons |
| Length | 17 feet 6 inches |
| Width | 9 feet 1.5 inches |
| Height | 9 feet 3 inches |
| Crew | 5 |
| | |
| Armour | 6.25 mm |
| Main armament | QF 3 pounder gun (47 mm) |
| Secondary armament | four 0.303 (7.7 mm) Hotchkiss M1914 machine guns two 0.303 Vickers machine guns |
| Engine | Armstrong Siddeley V-8 air-cooled petrol engine 90 hp (67 kW) |
| Suspension | helical spring |
| Operational range | 190 km |
| Speed | 15 mph |
Suspension
Despite being in general more conventional, in one aspect the Medium Mark I looked rather modern: instead of a high track run it possessed a low and flat suspension system with five bogies, each having a pair of small double wheels. The axles of these were too weakly constructed; as Major-General N.W. Duncan put it in his Medium Marks I-III: "(...) a perpetual nuisance. The axles were continuously breaking and the path of the Mark I tanks was littered with discarded wheels". To ease repairs the suspension was not protected by an armoured covering. There were two vertical helical springs of unequal length in each of the five bogie casings attached to the hull. In front and behind the normal ten road wheel pairs, there was a tension wheel pair. Ground pressure was very high, even though at 11.7 long tons the vehicle was not very heavy for its size.
Engine
All this was driven by an air-cooled 90 hp Armstrong Siddeley engine derived from an aircraft type. Surprisingly the hull was uncompartimentalised with the engine to the left of the driver, which Duncan laments as "an unbelievable retrograde step in view of war-time experience". The Medium Mark B and the Mark VIII had introduced compartmentalisation to reduce the debilitating effects of engine noise and fumes on the crew. However with the Medium Mark I considerations of ease of maintenance had taken precedence.
Transmission
The engine drove, via a multiple dry-plate clutch, a four-speed gearbox. It had no synchromesh and switching between gears without making it sound as if the entire vehicle was about to come apart, apparently posed a bit of a challenge to the driver. A propeller shaft connected the gearbox to a bevel box at the end of the tank which divided the power to a separate epicyclic gear for each track. These gears automatically provided extra emergency torsion to the normal first and second gear if the vehicle suddenly slowed down due to an obstacle or soft ground.
Fuel and oil
The petrol tanks were on top of them, so the fuel ducts had to run along the whole length of the vehicle, pumping fuel to a secondary tank that fed the engine by gravity. The engine was cooled and lubricated by oil; leakage was common and the original four-gallon reservoir had to be replaced by a 13.5 one. The tank could be electrically started, but only if the motor was already warm, so the first start had to be done by hand from the inside of the vehicle. Maximum speed was about 15 mph and the range about 120 miles.
Armament
There was a cylindrical bevelled turret on top of the hull that carried a "Quick Firing" three-pounder gun (47 mm calibre) and four ball mountings for Hotchkiss machine guns. A novel, unique feature was a three-man turret. This meant that commander was not distracted with neither loader's or gunner's tasks and could fully concentrate on maintaining situational awareness. This gave a huge potential combat advantage, but went largely unnoticed at the time. Non-Vickers tanks did not have this capability until the German Panzer III was developed in 1937. The practical importance of this feature is signified by the fact that later into the World War II, most of both sides tanks' designs either quickly switched to the three-man turret, or were abandoned as obsolete.
There was no co-axial machine gun. There was only room to operate one machine gun from the turret; normally one gun was switched between the respective mountings as the guns were removable. The turret machine gunner doubled as main gun loader. In each side of the hull was a Vickers machine gun, but there was only one gunner, also functioning as mechanic.
Body
The shape of the Mark I Medium hull was very distinctive. The back was a simple armoured box; the front plate was high and perfectly vertical. Between them, from the armoured hood of the driver at the right of the vehicle six armour plates fanned out to the left, making for a complex hull geometry at that side. In all the tank made an ungainly squat impression. The crew of five was only poorly protected by 6.25 mm plating, rivetted to the chassis, barely enough to counter the threat posed by light machine guns. With its many shot traps the vehicle was unable to withstand even anti-tank rifle fire and it had a high profile. The internal lay-out worsened this vulnerability as the petrol tanks were inside the main compartment.
