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Star RU-35 submachine gun, left side
Star RU-35 submachine gun, right side 
Star RU-35 submachine gun, close-up view on the controls (fire mode selector, left, and rate of fire selector, right) | Caliber | 9x23 Largo |
| Weight | 3.74 kg |
| Length (stock closed/open) | 900 mm |
| Barrel length | 269 mm |
| Rate of fire | 300 or 700 rounds per minute |
| Magazine capacity | 10, 30 or 40 rounds |
This submachine gun was developed by mid-1930s by famous Spanish arms-making company Bonifacio Echeverria SA, which operated under the trademark "Star". There were three slightly different model in the 1935 Star line of submachine guns: the RU-35, which had slow rate of fire of about 300 rounds per minute, the TN-35, which had fast rate of fire of about 700 rounds per minute, and the SI-35, which has dual (selectable) rate of fire. Otherwise all three weapons were similar, sharing same layout, same complicated delayed blowback action, and same overly complicated controls setup, consisting of two multi-position levers on the left side of the receiver. These submachine guns were manufactured in Spain and used by Guarda Civil. During the WW2, a version of this submachine gun was tested in USA and UK under the name "Atlantic", but was rejected on the grounds of the complexity and excessive costs of manufacture.
Star RU-35 / SI-35 submachine gun utilizes delayed (retarded) blowback operation, using two-part bolt with special locking piece, which temporary locks the bolt head to the receiver upon the early stages of recoil. Gun fires from open bolt, in full and semi-automatic modes. The SI-35 version has additional rate of fire reducer which is controlled by the rear switch on the left side of the receiver (it also doubles as a safety). Forward switch controls modes of fire (semi-automatic or full automatic). Feed is from detachable box magazines, which were supplied in various capacities. Rear sight was adjustable for range from 50 and up to very optimistic 1000 meters range. Gun was fitted with wooden stock, barrel was enclosed into slotted jacket, which also carried muzzle brake - compensator and a bayonet lug.