In October 1988, the German MoD awarded Rheinmetaii a full-scale development contract for the MK 35/50 mm Rh 503 cannon.

Prime contractor is Rheinmetaii heading a team that includes Mauser (cannon), Diehl (HE ammunition), Honeywell (time fuze/time setting system) and Oerlikon Contraves/Heckler & Koch (ammunition transport system).

Before awarding this contract, the German MoD compared the effectiveness of existing 25 mm, 35 mm and 60 mm calibre weapons against a variety of targets and came to the conclusion that a new weapon was required.

The automatic cannon MK 35/50 mm Rh 503 is required to engage soft and area targets as well as future medium armour beyond the year 2000 and to contribute to all-arms air defence, especially attack helicopters, out to a range of 2,000 m.

The original application of the Rheinmetaii Cannon MK 35/50 Rh 503 was the new Marder 2 infantry combat vehicle. By early 1992 a single prototype of this had been completed by the now Krauss-Maffei Wegmann, this being fitted with the two-man power-operated turret TS 503 designed and built by Rheinmetaii. Details of the turret are given in the AFV turrets and cupolas section.

In December 1992, the German Ministry of Defence announced that development of the Marder 2 was being stopped as part of an economy measure.

The original intention was to develop both 35 and 50 mm versions but development work was subsequently concentrated on the former version because of changing operational requirements. The 50 mm version has, however, been test fired and could have been backfitted if required in the future if the threat changed.

Although Rheinmetaii is the prime contractor for this weapon system, Mauser has now been taken over by Rheinmetaii and all medium calibre weapons development (including ammunition) is concentrated at the facilities of Mauser-Werke Oberndorf Waffensysteme GmbH.

The Rheinmetaii MK 35/50 mm Rh 503 is an externally powered weapon that initially fires existing bottle-shaped 35 mm ammunition, which is already in service with Germany and a number of other NATO countries, as well as new Rheinmetaii 35 mm KE and Diehl HE rounds.

The 35 mm barrel can, however, be replaced in 5 minutes by a 50 mm barrel to allow it to fire new 50 mm ammunition, which corresponds to the base diameter and length of the 35 mm round. The new round has no shoulders but instead has a nearly cylindrical form from the base of the case to the tip of the projectile. No other modifications regarding ammunition stowage and feeding are required.

As previously stated, the Rh 503 is an externally powered weapon and all functional components are positively controlled which makes the function of the weapon reliable and independent of ammunition gas pressure level.

The rate of fire can be selected to within a range of 150 to 400 rds/min, and single shots can be fired. If the main power supply fails, then drive can be powered by a battery. In addition, manual operation for single-shot fire is also available.

The modular design of the weapon (recoiling cannon assembly and drive assembly) keeps maintenance to a low level. The rounds are fed from both sides without links and immediate ammunition change 'without a wrong round' is provided. The empty cartridge case is not ejected by a stroke as happens with gas-operated weapons but slides out of the front in a straight line. Therefore, the ports for expelling the cases forward out of the turret have considerably smaller cross-sections than conventional automatic cannons. This offers additional design advantages relating to the shield and the arrangement of the weapon in the turret.

In case of ammunition misfire, the cannon is automatically stopped in the safe position by an interlock device. Firing can be continued immediately after the misfired round is ejected.

Development. At present there is no production application for this 35/50 mm weapon.