Overcoming water barriers by troops during military operations is still one of the most difficult tasks of engineering support, but also the choose of its type: landing, ferry, or bridge.
After WWI, various tests were carried out in Poland, France and the United States, but it was in 1929 that Vickers-Armstrong created the first amphibious tank called "Vickers - Carden-Lloyd amphibious tank", types A4E11 and A4E12, which is considered to be the ancestor of all vehicles of this class. Very light, fitted with floats under the hull and wooden beams above the tracks, the hull was welded. Purchased 8 copies by Russia, it will be used as a model for the T-37A, floating tank of N.N. Kozyreva, built in 1900 copies from 1933 to 1936 in the factory N ° 37 in Moscow.
We found ourselves in the Far East in the summer of 1934, during an exercise in which 23 T-37A tanks from the Soviet Army crossed Lake Hanko for 60 km. One of the tanks sank. The other tanks reached the opposite bank, but the grip of the tracks left something to be desired on the banks, the grasses and algae surrounding the propellers.
At that time, Anatoly Fedorovich Kravtsev was part of the OKDVA group, Special Red Banner Far Eastern Army, graduate engineer, draws the conclusions: the pressure of the tracks on the ground should not exceed 0.35-0.45 kg / cm², necessary speed above 6 km / h and a breakwater shield is required.
In 1934-38, under the direction of A. Kravtsev, work was carried out to ensure the passage of military equipment through the water barriers. A. Kravtsev's first ferry boat for BT-5 is made with two regular AZ boats and special amphibious tracks have been manufactured with removable articulated plates. The test in the Vladivostock region gave fairly good results. The relatively long installation and fixing time of AZ boats on the tank body took about 15 to 20 minutes, and disassembly took another 5 to 8 minutes, plus the transportation of equipment.
A. Kravtsev also imagined a rubberized rampart around the tank, like the WWII DD tank.
After a while, A. Kravtsev’ research group, on the instructions of the OKDVA command, developed a new individual way of overcoming water barriers. This time, two metal cigar-shaped floats were attached to the tank which developed a speed of about 14 km / h on water, which was an important achievement at the time.
In 1938 A. Kravstev was in Moscow.
Crossing studies only resume after the war.
The existing crossing facilities were delivered mainly in disassembled form and their preparation in combat was very laborious. The transportation of these funds to their destination was limited, and often they were simply brought ashore by soldiers in their arms.
For the edges of banks it was necessary to provide tracked vehicles. A promising basis for the implementation of A. Kravtsev's ideas was the tracked artillery tractor from the Mytishchi No. 40 factory, which had recently been put into production.
A. Kravtsev studied all the possibilities for the new amphibious vehicle whose engine was found in the middle of its length. Two propeller tunnels led to the back.
On December 3, 1947, a special study office for engineering troops (OKB IV) was created.
As there was no national analogue and information on foreign vehicles was extremely scarce, the A. Kravtsev’s team started from scratch: there was no theoretical study of the hydrodynamics of tracked and wheeled floating vehicles, calculation methods and manufacturing techniques for thin-walled metal structures; there was no practical experience in transporting artillery systems and vehicles weighing approximately 5 ton with high dynamic loads, loading, unloading and mooring of equipment transported by land and river carriers; there were no operational requirements for the design, service life and maintainability of the amphibious machine.
Throughout the study, in addition to many technical problems, security issues were addressed very seriously. Thus, for conveyors, automobiles and artillery systems that create concentrated loads on the platform, a gauge structure was used: two powerful box-shaped duralumin beams with 0.68 m vertical limiters wide have been installed as flooring. Six mooring earrings were welded to each of them.
Initially, American GMC-4-71 diesel engines were fitted to the prototypes while awaiting a copy of this engine: the YaAZ M-204V.
The track carrying rollers went from 10 to 14 because the conveyor reached 12.5-14.5 t instead of 8.5 t for the Mytishchi artillery tractor, which increased the length of the track. The specific ground pressure of the conveyor with a load of 3 ton should not exceed 0.45 kgf / cm 2.
The loading on the platform was carried out by a tailgate and folding ramps. There were many technical problems: tracks (load wheels and return rollers), freeboard problem and addition of removable walls, difficult welding, sealing of the rear panel, vibrations, numerous stiffening reinforcements, lengthening of the total length.
Three prototypes were built in Stalingrad.
After completing the factory tests, the conveyor was transferred to the test site. They took place from July to August 1948 in the suburbs of Moscow on Lake Pirogovsky and on the Dniester.
In May-June 1949, three K-61 pre-production conveyors were prepared at the Stalingrad tractor plant for further testing. On May 16, 1950, the K-61 floating crawler conveyor was adopted and its production entrusted to the Kryukovsky car manufacturing plant.
On October 18, 1952, the more severe tests continued.
After carrying out control tests, the amphibious tracked vehicle K-61 was produced by the Krukovka car factory until 1958. Then the company began to develop a more advanced machine, the future PTS.
In the same year, production of K-61 was transferred to the Izhevsk Stroymashina factory. Izhevtsy presented the first vehicles on December 31, 1959, but testing continued in 1960.
Production of K-61 in Izhevsk lasted until 1965 in batches of 10 to 15 units per month. The total number of K61 produced would be around 1000 to 1500 copies.
In the mid-1950s, it was necessary to test in the field the possibility of creating ferries and floating bridges using engineering means to cross the Desna. Thus, it was calculated that with 8 to 14 people, we can moor the ferry from two K-61s in 5 minutes plus the installation of ramps for 25-30 minutes, and on three K-61s, respectively, for 10-15 minutes and 25-35 minutes.
For the services rendered to his country, Colonel-engineer Anatoly Kravtsev won the State Prize, Ph.D. In the 1930s, he created devices for crossing water barriers by tanks, a device for the air transport of T-27 holds, remote-controlled demolition tanks, cyclone and multi-cyclone air purifiers for the engines of T-34 and KV tanks. After the end of World War II, the Special Design Office of the Engineering Troops under the leadership of AF. Kravtsev developed the floating carrier K-61 on tracks, the tank carrier K-69, the self-propelled tracked ferry K- 71, the K-73 self-propelled airborne support, the K-90 amphibious tank and the K-78 amphibious armored personnel carrier. After his resignation, A.F. Kravtsev taught at MADI, actively participating in the work of the students design office.
The K-61 floating tracked conveyor has become the ancestor of a whole branch of domestic engineering vehicles. Many design solutions proposed by its chief designer A.F. Kravtsev have become classic and are still used to create ferry facilities.
The K-61 transporter was in service with the Soviet Army and many countries. After the adoption by the Army of more advanced floating conveyors, the K-61 was returned to work in the national economy, where they were used by geologists, builders, fishermen, railway workers.
Anatoly Fedorovich Kravtsev received the State Prize of the USSR in 1958 for the creation of the K-61 floating tracked conveyor.