The Russian railways used European (British) buffers and couplings from their inception, albeit with the buffers at a slightly wider spacing due to the slightly wider gauge. These couplings had three main limitations. Firstly the load was limited. Secondly, the couplings weren't automatic like the American AAR. Thirdly, the buffers could get buffer-locked and cause accidents.
It took a while to find a replacement. One option was to copy the AAR coupling, as Japan (1922), Australia (1915) and other countries were starting to do, or to devise something else. The Soviets were not afraid to copy, as they had imported many engines and engineers during the various five year plans. In the end they chose the SA3, although implementation was delayed by WWII.
In the late 1920s, the UIC had established a working group for the replacement of the chain link coupler, which restricts the efficiency of freight railroads in a major way. Many railroads ran prototypes. In Germany, coal trains with Scharfenberg couplers yielded unfavourable results in winter weather, other railroads did similar tests. But the UIC wasn't able to agree on one replacement. This failure of the UIC, which hampers freight operation in Europe even today, led to the decision of the Soviet Union, to move forward without a standard being achieved in the talks.
The coupler was named SA-3. This type of coupler has been standardized for the railways in the Soviet Union, after World War II.
Further tests were carried out in the 1950s.
The benefit of this coupler: About 5000-6000 metric tons heavy could be hauled. This was a good impulse for the Soviet industries, because the transport capacities wer doubled.
Helper locomotives at the end of the train are rarely used in the countries of the former Soviet Union. The load of the freight per train is not as heavy as on American railways. This is due to the 3 kV DC electrification system. Most of the catenary in the former Soviet Union is fed with 3 kV DC and its construction (except some lines around Moscow) does not allow more than 6000 kW per electric section (one locomotive has power effort from 3000 to 6000 kW).
Although the SA-3 coupler is primarily used in the countries of the former Soviet Union, they are visible everyday at the transhipping stations, at the eastern borders of the European Union (Poland, Slovakia and Hungary). Since bogie changing-technology has progressed, this allows for cars with SA-3 coupler to regulary operate on the standard gauge tracks. A special converter car is inserted between standard and broad gauge cars for this operation, with different couplers (SA-3 and standard) on either end. Although these coupling freight cars (light blue coloured at the Slovak Cargo Railways) have room for cargo, they are always operated empty.
On the broad gauge railway line between Košice and Uzhhorod, Ukraine, of which the major part is on Slovakian territory, SA3 couplings are used exclusively. The railway is used for ore and coal transports from Kryvyi Rih, Ukraine to the US Steel mill in Košice and coal to the power plant of Vojany. In 2008, this line is to be extended into Austria.
In addition, the heavy iron ore trains on the Swedish Malmbanan began to use SA3 couplings in 1969 after problems with snapping chain couplers and a need for ever increasing capacity with higher train weights. Today, IORE locomotives haul 68 120-ton carriages with a total weight of over 8000-ton over gradients of 10 permille in harsh weather conditions, from the LKAB-mine in Kiruna to the ice-free harbour of Narvik, Norway using couplings of the SA3 type without any problem.
The new European Automatic Center Coupler (C-AK) has been based on this coupler, with the extended features of automatic brake and electric couplings. It also has vertical stability added, so that the coupling cannot fall down and damage the tracks or causing a derailment. It is compatible with the standard SA3 coupler and has the buffers needed for use with the standard chain couplings.
Other countries using the SA3 include: