Russian military inventions tend toward the brutally practical: tanks, planes, and guns that are cheap and easy to produce. Indeed, in WWII, the Soviet Union overwhelmed Germany with endless waves of T-34 tanks, fighter planes, and infantry armed with cheap submachine guns. Russia was very inventive and unorthodox in its creation of wartime vehicles and weapons.
Designing a tank or plane that can be reproduced tens of thousands of times takes experimentation and a willingness to embrace unconventional concepts. Combine this with the traditional tendency of Russian engineers to come up with unique ideas and worry about how to mass-produce them later, and you have a climate ripe for unique weapons. So in the 20th century, Russia led the way in designing original, unwieldy, and truly outside-the-box tanks, planes, weapons, and ships. Their designers liked putting wings on things, leading to inventions like flying tanks, flying subs, flying aircraft carriers, and even ships with wings.
Many of these ideas never got past the blueprint stage, though a few saw action in WWII. The Russians were determined, so no matter how unusual something was, if it worked, they used it. Yet, over time, many proved to be unsuccessful and ended up being ultimately forgotten.
A completely impractical tank design, the Tsar Tank was a huge armored vehicle designed like a giant reverse tricycle. It had huge front wheels measuring 30 feet in diameter and a small back wheel for balance.
Designed to be bristling with weapons and able to traverse any kind of terrain, the machine turned out to be slow and prone to breakdowns, mostly due to its small rear wheel. It also would have been an easy target, as it had no ability to carry armor and its wheels were unprotected. A prototype was built in 1914, but never got past that stage.
The arms race between the US and the Soviet Union didn't end at missiles and ships - it extended to experimental planes with no practical application. So when the US started developing a nuclear-powered bomber, the Convair NB-36H Crusader, Russia jumped in with their own designs. Tupolev engineers took one of their existing Tu-95 bombers and fitted it with a small nuclear reactor and shielding to protect the crew.
The LAL made over 40 test flights, but most with the reactor turned off. Concerns about the effectiveness of the shielding never went away. A second version, the Tu-119, was started, but the program was canceled due to cost and environmental concerns. These are the same reasons the US program was canceled.
Pondering a way to transport troops over inhospitable ground, Cold War engineers developed the idea of using giant corkscrews as treads.
The problem was that while the tank could move decently through muddy or snowy ground, it was useless on roads or on flat, hard ground. It also could only go forward or backwards, couldn't turn, and was both incredibly slow and prone to breakdowns. The Soviets did use some in Arctic areas, but found them to be highly impractical in most other environmental contexts.
The Zveno represented the Soviet experiment to attach smaller parasite fighters to a larger host plane. About 10 Zveno planes were built, typically using huge TB-3 bombers and a variety of smaller fighters. All were designed to have the fighter engines running, and the thrust of the bomber would give the initial push to the fighters, which would attack targets and fly back to their bases.
The Zvenos flew about 30 missions in the early stages of WWII, often performing well. Three parasite fighters were shot down, but never one of the hosts. The planes were retired when the small fighters they carried became obsolete.