Soviet Amphibious Assault Submarines

After the World War II, the Soviet Union experimented with various submarine technologies. Many of these experimental submarines aimed to bridge the gap between a submarine and a landing craft, essentially creating an amphibious submarine. Although the designs looked very good in theory, their practicality often lacked. Being able to carry large amounts of cargo, most of these submarines also had nuclear reactors planned as part of the design, effectively enabling them to stay submerged for months at a time.
During World War II, converted submarines were successfully used for transporting troops and supplies. The original idea had been born when fleets of submarines were used to supply the beleaguered city of Sevastopol with munitions, bombs and soldiers. These very same submarines had been used to evacuate wounded troops, woman and children. It was based on this success that formed the functional keystone which all subsequent projects were based.
Various design proposals or projects, were been set forth throughout the course of the Cold War. One such project, which never made it past the design phase was Project 621. This enormous underwater ship would have had a displacement of almost 6,000 tons, one of the largest submarines proposed at that time. The designers aimed this sub to be an almost carrier-like vessel, being able to carry a full infantry battalion. This would have included 745 troops, 3 fighter aircraft, various trucks and cannons and to top it all off, ten T-34 tanks. Unloading this array of cargo would see the submarine beaching, except for the aircraft which had to be catapult-launched.

Project 621 design courtesy of Global Security

The Soviets continued to work on this idea, even if they did not reach construction on the first project. The second project, named Project 664, was to be even larger than 621, expanding on its duties by also aiming to achieve in-route replenishment of various other submarines. Liquid cargo would include 1,000 tons of diesel or aviation fuel, 60 tons of oil, 75 tons of drinking water and a total of 31 tons of food. This project had been one of the few which successfully entered the construction phase, but its long list of requirements raising engineering difficulties, with some solutions creating problems for other functions. Construction started on this submarine at the docks of Severodvinsk. The design called for a nuclear powered sub capable of replenishment mine-laying and transport. This design however never had the nuclear reactor installed or construction finished.
The next Soviet project which had a high chance of success was Project 748. Designed as six different variants it ranged in size from 8,000 to 11,000 tons. This too was to be a nuclear powered sub, but no active replenishment duties had been planned for this sub. Instead, it was only to be used as a transport vessel, equipped with an armament of self defence. Going back to its 621 roots, it was designed to carry a total of 470 troops, together with twenty BTR-60 personnel carrier/tank combos. Designated the BTR or Bronetransporter, this armoured carrier could carry a total of 17 men including the gunner and driver. Shortly into production however, the decision was made to concentrate on yet another submarine effort and Project 748 was scrapped in the early 1970s.
The final project, named Project 717 was to be an all out achiever yet again. Specifications called for support of up to 800 soldiers, four armoured vehicles, a range of cargo and twenty BTR’s. Design called additionally for the ability to lay mines and evacuate troops. It was to be the largest submarine ever to be built at that stage, with a total displacement of 17,600 tons. The design was pursued to the point of full scale mock-ups already having been created. But as usual yet another project came up. This was to be the last Soviet initiative in developing an amphibious assault sub.