Description

The armoured draisine Tatra T18 was two-axle light rail vehicle. A chassis frame, riveted from steel profiles, was seated upon axles, sprung by helical springs. Axles were nested in ball bearings. In a middle of the frame, there was a tranversal air-cooled flat boxer engine, with a cooling fan and a mechanical gearbox (two gears in both directions). Only one (rear) axle was driven by a chain gear (it should be noted, that Polish military regulations claimed, that both axles were driven, what contradicts with Czech sources and plans – if it is true, maybe they were modified afterwards, although there has been no such information revealed). A fuel tank, 80 l capacity, was in the frame, behind front axle. Upon the frame there were also sandboxes to improve adhesion, operated by drivers (two according to Czech monograph, pouring sand only before left front wheel in drive direction, or four according to Polish regulation).

The body was made of armour sheets, screwed to a body frame. On a roof, there was a cylindrical turret, of 115 cm internal diameter and 46 cm height, running upon a ball bearing. In both hull sides there were rectangular entrance hatches. A small round hatch (50 cm diameter) was in the turret’s roof. The draisine had doubled driver posts, on both ends, slightly to the right of a longitudinal axis. Each driver had only one vision slot before him, covered with an armoured hatch. There were no other vision devices in the hull, including none for side observation. Only in the turret there were four vision slots all around, covered with hatches. As a result, observation conditions for the crew were apparenlty poor. Each driver had three pedals (acceleration, clutch and brake), a crank of a main brake to the right, and a gear stick and throttle and ignition levers to the left. The chassis frame was covered with a wooden floor, on which drivers sat (the floor was 67 cm above rails). There are no details, how the drivers’ seats were made; probably they had pads with no back support. A central section of the floor was removable for engine access. Above the central section there was a rotating gunners’ seat on a tripod. There was also a small flap in the floor, on one side, for starting of the engine with a crank from the inside. It is not clear how a lowered floor under drivers’ legs was made (it is not indicated on factory sketches) – there might have been a partial 5 mm armoured plate under part of the vehicle, screwed to the frame from an underside, as is suggested by Polish regulation.

(The Polish military regulation claimed generally, that the draisine had 5 mm armoured floor on a whole underside, with cut-outs for wheels, but there is no such mention in Czech monograph, and moreover, such floor would demand at least a big opening in a centre for jack arms and engine cooling, and also openings for axle suspension racks and their longitudinal joints, and it would also make a chassis maintenance difficult. It is possible, that the information was partially true, and the draisine had partial armoured floor, especially in ends. As we have mentioned, the regulation contradicts also in a number of axis driven and sandboxes).

The draisine was connected to other wagons with a simple coupler shank fitted in an upper part of a nose. In the second half of 1930s Polish drasines were additionally fitted with the second coupling, placed low on the nose, to connect with R and TK type draisines. Due to a weak engine, the Tatra could tow only empty rail runners of TK draisines, without tankettes. The draisine had 6V electric wiring, with a dynamo and 100 Ah battery. The draisine was equipped with two prominent armoured Bosch headlights on each end, with 65 mm armoured glass, giving white or red light (the Czechoslovak draisine had headlights covered with armoured flaps). It also had one removable searchlight on a mast upon the turret (the Czechoslovak draisine had a permanent small lamp on the turret). The engine had Bosch electric starter. Only the Czechoslovak draisine had an electric pneumatic horn, placed low on one side. They were not fitted with a radio and there are no reports, that it was considered (Magnuski suggested, that the draisines used in 1939 were probably fitted with a short-range radio N2/c, but there is no evidence to support this theory).

The draisine was fitted with a mechanical device to move the vehicle to a parallel track by the crew’s means. It consisted of a screw jack under the engine, a turntable and two auxiliary rails. The turntable, connected to two profiles, was put under the vehicle, which was next lifted by the jack. A crank of the jack stuck out from a rear armour. Its rotating shaft moved two levers, through screw gears, so they were pushing the jack base downwards. When lifted, the vehicle was turned at 90 degrees, and the auxiliary rails were put under its wheels, to drive upon the parallel track. On the parallel track the operation repeated in reversed order, and the draisine was lowered onto the track. Polish draisines were initially fitted with two short rails, carried on one side of the vehicle, but soon they were replaced with four longer rails, carried lower on both sides and normally serving as side steps each (they were joined together by two to create longer sections). In Polish draisines, the turntable was hung on one side during transport, next to the rails; in the Czechoslovak one it was of a slightly different shape and carried upon a rear horizontal armour.

The crew according to publications was 3 to 5 soldiers, including at least a commander-gunner and two drivers. There is no information however, how numerous was regular crew. Some publications claim, that there were two observers, but they would have no observation devices in the hull, while the turret was occupied by one or two gunners. Moreover, the draisine was very cramped inside, and it seems from plans, that there was no place to sit to the left of the drivers, where they had gear sticks and throttle and ignition levers. It is known, that the Czechoslovak draisine was used with four-men crew at times. It seems, that draisines in Polish service were armed with one machine gun, and three crewmen were the most practical.

An armament could be two independent machine guns mounted in two simple fork mountings in gun ports in the turret’s face, with open sights. In the Polish service, a single air-cooled 7.92 mm wz. 25 Hotchkiss machine gun was typically used. There is an official photograph of a configuration with one air-cooled 7.92 mm wz. 25 MG and one water-cooled wz. 08 Maxim 7.92 mm MG, but it does not seem to be used in practice, although the regulation from 1938 claimed generally, that the Tatra’s armament were « two MGs ». Apparently two gunners could have been accommodated in the turret, but it does not seem practical, considering a confined space inside, and the draisine’s primary purpose, which was reconnaissance, not fire support. On peacetime service photographs the draisines are seen with one wz.25 MG or without any armament at all, while on wartime photographs of abandoned draisines the armament has been dismounted. The single Czechoslovak draisine was used (at least for demonstration purposes) with two water-cooled 7.92 mm machine guns vz.24 Schwarzlose, probably manned by two gunners.

The machine guns could theoretically be used for anti-aircraft fire, after mounting in a special mount, firing upwards through a round hatch in turret’s roof, 50 cm diameter, but it is doubtful if it could be of any efficience, with a very limited angle of fire and of observation. It is not clear, if armour strips above gun mountings could be simply raised for higher elevation in standard mountings. Polish regulation mentions such possibility, and the strips above machine guns are apparently separate, but the regulation does not reveal more details, and there are not known any photographs in such configuration. It should be noted, that the Germans modified armour above gun ports in their draisine, probably for bigger elevation, but the details are not clear. Presumably some standard German MG could have been mounted by them, eg. MG 15 or MG 34.

Armour according to Czech data was: hull 6 mm (immune to ordinary « S » Mauser rifle bullets from above 200 m), turret 8 mm (immune to « S » rifle bullets from above 100 m). The Polish regulations claimed, that the armour was « about 8 mm », protecting against ordinary bullets from rifles and machineguns and artillery splinters[10]. During factory trials of the draisines, the first set of armour plates, made by Vitkovice Ironworks (Vítkovické železárny), was pierced, and the factory had to find a better supplier – Škoda works from Pilsen).

Specifications:
Weight (empty) – 3.7 t (Polish sources: 3.45 t); maximum weight – 5.27 t;
Dimensions: length – 3.675 m (with the jack crank; Polish sources: 3.55 m), width – 1,75 m (hull only, without external racks), height – 2.1 m; wheelbase – 1.5 m (59 in); wheel diameter – 500 mm.
Engine – Tatra T12: power output 12HP (8.82 kW), capacity 1056 ccm, petrol, 4-stroke, 2-cylinder, boxer, air-cooled, bore × stroke 82×100 mm.
Fuel tank – 80 l; fuel consumption – 9-10 l/100 km.
Top speed – 50 km/h in both directions (Polish sources – 45 km/h), range – 700 km, power-to-weight ratio – up to 3.2 HP/t.

Source : derela.pl