In the beginning of 70s military leadership of Soviet Union had a great interest in laser weapon development. Laser equipment was planned to put in space platforms, stations and aircrafts.
All the built units were based on stationary sources of energy and didn't meet the requirment of military space - full autonomy. This also didn't allow designers to carry out rigorous test. The government of the USSR ordered the Navy to test and work out autonomy. Laser gun which was figured in all documents as MSU (powerful propulsion unit) was decided to be installed to a ship.
In 1976 Sergey Gorshkov, a chairman of Navy approved rebuilding of landing ship 770 SDK-20 to experimental ship called project 10030 "Foros". It was planned to test here "Akvilon" - a laser complex which targets were optical-electron units and opponent ship crew.
Process of rebuilding lasted for 8 years. Ship's hull needed to be imroved because of "Akvilon" huge size and weight. At last in September of 1984 ship OS-90 "Foros" joined The Black Sea Fleet of the USSR.