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Railways in Russia used European (British) buffers and chain couplings from their inception. These couplings had three main limitations. Firstly the load was limited. Secondly, the couplings were not automatic like the North American Janney AAR coupler. Thirdly, the buffers could get buffer-locked and cause accidents. Advantages and disadvantages of these couplings are intermediate between Janney AAR couplers and Scharfenberg couplers.
It took a while to find a replacement. One option was to copy the Janney 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 World War II.
The Willison coupler was patented by John Willison from Derby, England. It was registered in 1910, and approved in USA 1916, and in Germany. The company Knorr bought it and it started to be used in Germany for some heavy trains and some suburban trains in Paris. The Soviet Union needed a new coupler and decided to used this coupler.
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 was not able to agree on one replacement. This failure of the UIC, which hampers freight operation in Europe even today, led to the decision by the Soviet Union to move forward without a standard being achieved in the talks.
The coupler was named SA-3. This type of coupler was standardized for the railways in the Soviet Union after World War II.
Further tests were carried out in the 1950s.
Operation of this coupler
The benefit of this coupler: About 5,000–6,000 tonnes (4,900–5,900 long tons; 5,500–6,600 short tons) could be hauled. This was a good impulse for the Soviet industries, because the transport capacities were 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 6,000 kW (8,046 hp) per electric section (one locomotive has power effort from 3,000 to 6,000 kW or 4,023 to 8,046 hp).
Although the SA-3 coupler is primarily used in the countries of the former Soviet Union, they are visible every day at the transshipping 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 regularly 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.
If the vehicle fitted with the SA3 retains its buffers, then a special adapter allows that vehicle to couple to another vehicle fitted with buffers and chains, provided that the buffers have the same spacing or gauge. This appears to be done in Iran.
On the Uzhhorod–Košice broad-gauge track 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 trains of 68 hopper cars of 120 tonnes (120 long tons; 130 short tons) with a total weight of over 8,000 tonnes (7,900 long tons; 8,800 short tons) over gradients of 10 per-mille (1%) 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.[discuss] The earlier SJ Dm3 locomotives have buffers fitted, therefore they can couple with cars (or locomotives for transportation purposes) with chainlink coupler.
Worldwide, the heaviest trains, of around 30,000 tonnes (30,000 long tons; 33,000 short tons), operate with Janney AAR coupling. The SA3 is not used for such loads—the European single locomotive haulage record stands at 12,000 tonnes (12,000 long tons; 13,000 short tons), by a British Rail Class 59. New railways are mostly electrified at 25 kV 50 Hz AC, which allows higher power than 3 kV DC, so records may yet be challenged. New international links may also see the SA3 and Janney AAR coupling meet and it is unknown how this break-of-gauge will be resolved.
The new European Automatic Center Coupler (C-AKv) 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 cause a derailment. It is compatible with the standard SA3 coupler and will have buffers needed for use with the standard chain couplings under the long transition period. The electric plugs would be most useful with electronically controlled pneumatic brakes.
The former Soviet Union:
Other countries with extensive usage
- Finland, Rail transport in Finland
- Iraq, Iraqi Republic Railways
- Mongolia, Rail transport in Mongolia
- Turkey, Rail transport in Turkey
- Mauritania Railway Société Nationale Industrielle et Minière
- Gabon, Trans-Gabon Railway (called Willison coupler) 
- Sweden & Norway (Malmbanan/Ofotbanen); Used exclusively by heavy iron-ore trains.
- Australia; Miniature SA3 used on some sugarcane tramways and underground colliery railways.
- Slovakia (Uzhhorod–Košice broad-gauge track); Heavy iron-ore transports from Ukraine.
- Poland (Broad Gauge Metallurgy Line); The longest broad gauge railway line in Poland. It is used only for freight traffic, mainly iron ore and coal.