Project 904 Orlan class / A-90 Orlyonok
Amphibious landing craft

Wing-In-Ground (WIG) effect craft take advantage the fact that the aerodynamic efficiency of a wing, and particularly its lifting capacity, improves dramatically when is operated within approximately one-half of its span above ground or water, in what is termed ground effect. If the wing's natural accelerated flow passing over it is further accelerated by the high-velocity exhaust of a turbojet engine, the lifting capacity of the wing is even more greatly enhanced.

Several of the ORLYONOK (known in the U.S. by its NATO designator ORLAN) vehicles were constructed from the mid-1970s to the early 1980s to demonstrate an amphibious ekranoplan capability. Flight tests for these vehicles may have been conducted from the late 1970s until the present. One of the vehicles was reported to have crashed in the summer of 1992.

In 1966 the Central Hydrofoil Design Bureau under Rostislav Alekseev produced a gargantuan "ekranoplan" ("surface plane") combining the smooth hull form of a ship with stub wings, a large vertical fin and horizontal tail. The craft featured ten engines: eight mounted in two clusters of four directly behind the cockpit to provide augmented lift, and two on the vertical fin to provide cruise power. This machine, which American intelligence organizations dubbed the Caspian Sea Monster, could lift 540 tons and cruise at over 300 mph at an altitude of over 10 feet.

Alekseev developed a smaller military WIG, the Lun ("Dove"), armed with six large antishipping cruise missiles perched unaerodynamically on its back. This led to the jet-and-turboprop-powered Orlyonok ("Little Eagle," NATO name Orlan), intended as an amphibious assault craft. The apparent success of these machines hid some very real problems, not least of which were serious stability and control deficiencies, as well as tremendous power requirements to get off the water.

The Caspian Sea Monster's successors, including the Lun (Hen Harrier) and the Orlyonok (Eaglet), were much smaller and lighter and were used both for military and civilian purposes. In 1972 Alekseyev developed his own ideas and created an amphibious version of the ground effect vehicle called the "Orlyonok", aka the A-90. The A-90 Orlyonok was one of the most successful ekranoplans. It was used for military purpose and for transferring cargo. The A-90's weight was 140 tons and it was 58 meters long. It could reach at least 400 kilometers per hour, and flew at an altitude ranging from five to ten meters.

The ship was able to cross from one end of the Caspian Sea to the other in one hour with up to 200 fully armed marines as well as two floating tanks (APC, IFV) and their crews on board. At the same time the vehicle already had the characteristics of a ground-effect aircraft: not only could it travel a few meters about the water's surface, but it also could ascend to a height of 300 meters. Orlyonok-type ground effect vehicles entered the service of the Navy of the USSR in 1979. A total of five A-90 vehicles were built. The last of them was decommissioned in 2007.

The first unit began testing in 1973, and the system entered service in 1979. The last flight was in October 1993, and the remaining units were believed to be in storage at Kaspiisk Naval Air Base.